How do I transfer custom code to a new website theme?

Store Design

Topic summary

Transferring existing custom code and a custom Shopify app to a new theme (theme = the store’s design/template) requires more than copy-paste due to differing file structures and coding conventions. Custom app logic tied to the front-end may also change behavior.

Key steps:

  • Contact the original developers to help port the customizations and ensure compatibility.
  • Create a full backup of the current theme and all custom code/app files before changes.
  • Compare old vs. new theme file structures; place relevant code into the corresponding files.
  • Test the new theme thoroughly; adjust code for compatibility and fix visual issues (logos, fields, icons, custom blocks).
  • Double-check that all customizations work as intended.

Additional guidance: If you’re not technically experienced, hire a reliable Shopify development company to manage the migration.

Outcome: No definitive resolution yet; the thread provides actionable next steps and stresses careful testing and professional assistance to avoid breakage.

Summarized with AI on January 30. AI used: gpt-5.
1

Hi everyone,

Some month ago, a company created a custom code and an custom app for us, I would love to change my Webpage theme, I’m not sure how to transmit this changes to a new Theme.

I tried to copy paste some of the code, However i’m not sure if I’m doing right.

Would love some advice.

Best,

Gesa

2

hello there

If you are changing your website theme, it’s important to ensure that your custom code and app are compatible with the new theme. Simply copying and pasting the code may not work if the new theme has different file structures or uses different coding conventions.

Here are some steps you can take to transfer your customizations to a new theme:

  1. Contact the company that developed the custom code and app and ask for their assistance in transferring the customizations to the new theme. They may be able to provide guidance or make the necessary changes for you.

  2. Create a backup of your current website theme and all custom code and app files before making any changes.

  3. Compare the file structures of your current and new themes to identify any differences that may affect your customizations.

  4. Copy and paste the relevant portions of the custom code and app into the corresponding files in the new theme.

  5. Test the new theme thoroughly to ensure that all customizations are working correctly.

  6. Make any necessary adjustments or modifications to the custom code and app to ensure compatibility with the new theme.

  7. Double-check that all customizations have been successfully transferred and are functioning as expected.

1 Like
3

Hello @gesam ,

Changing a theme is not a trivial thing at all. It can cause visual issues related to the placement of logo, fields, icons and any blocks, especially, if they are added as custom. It may also influence behaviour of apps which add custom logic to the front-end.

If you are not a technically aware person yourself, you should find a reliable Shopify development company which understands possible bottlenecks and can perform this process smoothly.

Best regards,
Anastasia

1 Like