Question: Is it possible to change the ID of custom fields? I have custom transaction body fields with IDs like “custbody5” that I’d love to change to something more easy to recognize

Yes make sure it’s not being used in script or some integration else you must amend them too.

Do I have to make the update through a CSV import? That field is not editable

You should see a Change ID button when in edit mode on the custom field

too easy! Thank you!