In this case I would suggest one of the following:
-
during the rolling migration, base your instance off your fork. If you want to include new functionality, just sync your fork with upstream on a regular basis. When the migration is done, switch back to
discourse/discourse -
clone your repo outside docker and copy the files in. Do it after a rebuild, otherwise the precompile script will find the repository unclean and the build will take much longer.
I think #1 would be the best.