I appreciate the detailed information, @Abdul Rehman.

The workaround provided by my colleague @ShiellaGraceA will work on the Standard Custom form styles. 

Currently, the Edit option for Imported Custom form styles is unavailable. You'll have to re-import the template once again, you can check the steps through this link: https://quickbooks.intuit.com/learn-support/global/importing-and-exporting-data/import-custom-form-s...

I can see how the edit option for Imported Custom form styles can be beneficial for you and your business. I’m sending feedback on your behalf straight to our developers for consideration in future product enhancements.

You may also visit our QuickBooks Online Blog to know more about our latest happenings. From there, you’ll get the recent news, features, and updates about QBO and what our Product Team is working on.

Please post again if you need any other help. Have a blissful day