I had the same problem today.
Try this as a workaround:
Role-renaming is kept, when you include users in your course-backup, to whom this renamed role "belongs".
- When using a course as a template, I enrol only one user.
- This user I give all the renamed roles. The user can be either the regular teacher of new courses oder a dummy user.
- For backup I include enroled users.
- Restore the backup to new course.
- Voilà, the renaming of the roles is present in the new course.
Hope, this works for you too.