Job theme-customisations-into-child-theme · revised 11 October 2026
Move edits made inside a WordPress theme into a child theme, so updates stop erasing them
Find every change made directly in a parent theme, move it into a child theme, and prove on staging that it works with the current parent, then the updated one, and can be switched back.
You might be seeing
- A theme update undid a colour, a layout tweak or a function
- The theme update has been postponed for months
- Nobody knows which files were edited
- A theme settings page shows no sign of the changes that appear on the site
No passwords, keys, card details or admin invites needed to start.
What usually happened
Edits made inside a parent theme's files live in the folder an update replaces. The next update erases them, so the site owner chooses between running an outdated theme and losing the changes. A child theme holds the changes separately, but moving them needs a full list of what was changed and care that settings and templates still line up.
Who it’s for: Owner or agency of a WordPress site whose theme was edited directly and whose theme updates are now postponed or have wiped out changes.
Usually starts when: A theme update removed a custom tweak, a security update is waiting but nobody dares to apply it, or a developer who edited the theme files has left.
The result: Every difference between your theme and the vendor's clean copy of the same version is either carried into a child theme or listed as dropped with your approval. On staging the child theme works with the current parent and then with the parent updated to its latest version, the named pages stay the same, and switching back restores the earlier state.
Check whether this job fits
A few short questions. Your answers stay on this page unless you choose to email them.
Checks you can run yourself
Find the theme's version
In the WordPress admin open Appearance, then Themes, and click the active theme.
Look for: The version number and whether it says "child theme of" anything. Share the version and theme name.
Ask who edited it
Ask anyone who has managed the site whether they changed files in the theme folder or only used its settings.
Look for: A name or a date. Even a vague answer helps find which files to check first.
What you get
- The difference list with a decision for each item: kept, dropped or needs your input
- The child theme as files, ready to install
- Before and after screenshots of the named pages at desktop and phone width
- A before and after table of menus and the theme's own settings, and a note on settings that need re-entering and why
- Steps for the live change in separate stages: switch to the child theme with the current parent, check, then update the parent, check, and the switch-back
Included
- One parent theme and one site, with a clean copy of the same theme version to compare against
- A written list of every file that differs from the clean copy
- A child theme holding the kept changes: template overrides, added code and custom styles
- A before and after comparison of menus and of what the theme stores for itself: Customizer settings, menu locations, widget placements and, for a block theme, Site Editor templates and Global Styles
- A staged test on staging: the child active with the current parent, then the parent updated to its latest version, with up to eight named pages checked after each step, and a tested switch-back
Not included
- Redesigning the theme or the site
- Fixing bugs in the original edits unless they stop the move
- Updating WordPress core or plugins
- Theme files that depend on a plugin you no longer have
- Making a site that already runs a child theme safe: that is a different job
- Applying the switch on the live site
How we know it’s done
Agreed with you before work starts. Each check produces evidence you keep.
Every file that differs between your theme and the clean copy of the same version appears in the difference list with a recorded decision
Evidence: The difference list and the comparison output
With the child theme active and the current parent version on staging, the named pages match their before screenshots on an agreed checklist at desktop and phone width
Evidence: Side-by-side screenshots and the checklist
With the parent then replaced by the latest vendor version on staging, the named pages still match their before screenshots on the same checklist
Evidence: Side-by-side screenshots and the checklist
After each of those two steps menus, menu locations, widget placements and Customizer settings match the before state, and for a block theme so do the Site Editor templates and Global Styles, or each difference is listed as needing re-entry
Evidence: A before and after table and, for a block theme, screenshots of the Site Editor's templates list and Global Styles before and after
After switching back to the original edited theme on staging, the named pages and the same settings table match the before state
Evidence: Side-by-side screenshots and the settings table
No new PHP error appears in the staging log with the child theme active during the test run
Evidence: Redacted log excerpt for the test window
Sign-off. You sign off after the staging checks pass; your site holder then takes and test-restores a backup, switches to the child theme with the current parent and confirms the named pages live, and only then applies the parent update and confirms them again.
If it fails. If the checks do not pass, you do not pay, and you keep the difference list.
When it fits, and when we stop
It fits when
- You can get a clean copy of the same version of the parent theme from its maker, and you hold the right to use it
- The edited theme files are available to us on a staging copy
- You can name up to eight pages that must look the same afterwards
- A staging copy exists
- Your site holder takes a full files-and-database backup before the live switch and has tried restoring it onto the staging copy or another non-public location
We stop and tell you if
- A clean copy of the same theme version cannot be obtained, so edits cannot be told apart from the original
- More than about thirty files differ: we quote a larger project
- The theme is already a child theme of another theme
- The edits include a plugin written inside the theme that needs rebuilding as a plugin
- The site is a multisite network, which is quoted separately
- No full files-and-database backup can be taken and restored before the live switch
What could go wrong
The restore point is the full backup your site holder takes and test-restores before the live switch. The quick undo is switching back to the original edited theme, which we rehearse on staging; the handover keeps a full copy of that theme. Some settings are stored against whichever theme is active, so menus and the theme's own settings are checked again after any switch.
Scroll the table sideways to read it all.
| Risk | How we handle it |
|---|---|
| Settings stored against the active theme do not follow the switch to the child theme | We record menus and the theme's own settings before the switch, compare them after each step on staging, and list anything to re-enter. For a block theme we also compare the Site Editor's templates and Global Styles, because a file comparison cannot find them. |
| The child theme and the parent update are applied together, so a difference cannot be traced to one of them | The live change is staged: switch to the child with the current parent, check, then update the parent and check again. |
| A kept change relied on a parent file that changed in the update | The staging test uses the latest parent version, and conflicts are shown in the note before anything goes live. |
| Copying the parent's code into the child causes duplicate function errors | We override only what must be different and add new code rather than copying the parent's. |
| The live switch loses something that cannot be recovered | Your site holder takes a full files-and-database backup and test-restores it first; the switch-back has been rehearsed on staging. |
A second reviewer checks the difference list is complete by running the comparison again, and reads every kept change that handles input or outputs data.
How we deliver
We arrange the work and independent review, then show you the result against the agreed checks. You keep authority over your systems.
- Set up the edited theme and the clean copy side by side on staging and list every differing file
- Agree with you what to keep, drop or clarify for each difference
- Build the child theme with the kept changes, using override files and enqueued styles instead of copying the parent's code
- Record menus and the theme's own settings (Customizer settings, menu locations, widget placements and, for a block theme, Site Editor templates and Global Styles), switch to the child theme with the current parent on staging and compare
- Run the page checks, then replace the parent with its latest version on staging and run them again
- Switch back to the original edited theme on staging and check that the pages and settings return to the recorded before state
- Independent review, then hand over the child theme, the list and the staged live steps
This is a one-off job, not emergency cover or a subscription. We confirm eligibility, the total price, a start window and a delivery date before you accept. Work starts only after agreed inputs, secure access, any licences and necessary permissions are in place. Hosting, plugin licence and supplier charges are excluded unless the written quote includes them. No charge or booking is created by an enquiry.
Need to keep it working?
Discuss trying each theme and plugin update on a staging copy before it goes live.
Ongoing work is separately scoped and quoted: no monitoring, response-time guarantee or automatic subscription is included in this job.
Explore an ongoing engineering lane, or mention the responsibility you need in your enquiry.
What you can check
This is a new service. We have not delivered this job for a client yet.
Other ways to get this done
- If the changes are only some added styling, many themes have a place for custom styles that survives updates. That can be enough without a child theme.
- WordPress documents child themes. If you are comfortable with files and know what was edited, the steps are in the theme handbook.
Questions
Why do I need a clean copy of the theme?
It is the only way to tell your edits from the original. Without it, a file that looks odd might be the maker's own code.
Will my settings survive?
We record menus and the theme's own settings before the switch, compare them after each step on staging and list anything that needs re-entering, instead of promising it. Some settings are stored against the active theme, so they can differ when a child theme becomes active.
Why is the live change in two steps?
If the child theme and the parent update are applied together and something changes, nobody can tell which caused it. Your site holder switches to the child with the current parent first, checks, and only then updates the parent.
Do I need a backup?
Yes. Your site holder takes a full files-and-database backup and test-restores it before the live switch. The job does not go live without that restore point.
Can I update the theme myself afterwards?
Yes, that is the point. The handover steps include a staging test routine for each update.
Send an enquiry
Send us
- The theme name, its version and where you got it
- Whether you know what was edited, who edited it and when
- The list of up to eight pages that must stay the same
- Whether the theme has a settings page or uses the Customizer or Site Editor
- The theme update you are waiting to apply
Later, once you agree
- A staging copy of the site including the edited theme files
- A clean copy of the same version of the parent theme, with your licence if it is paid
- A staging admin login, not your live one
- Your site holder's written confirmation, before the live switch, that a full files-and-database backup exists and has been restored once onto a non-public copy
- A company-controlled secure handoff agreed before access: no live passwords, keys, private code or customer records by ordinary email.
You keep the live site and the theme licence. We work on a staging copy; your site holder takes the backup, installs the child theme and updates the parent in the stages we set out.
Email fallback: open your mail app
If website submission is unavailable, review and send the fallback email yourself. An email fallback is not a website receipt. Or write to hello@syntheticindustry.ai with “theme-customisations-into-child-theme” as the subject.