Hey John-Scott,
I'm afraid but I don't see an obvious solution. There are 2 ways you could work on the issue, I don't like either:
1. remove all references to the "foo_tag" app from all migration files
2. make use of the MIGRATION_MODULES settings:
2.1. create a package "path.to.foo_tag_legacy"
2.2. inside create an empty migration "0001_initial"
2.3. define MIGRATION_MODULES={"foo_tag": "path.to.foo_tag_legacy"}
As said, both seem ugly to me. I don't know which way I'd proceed.
You might get it working by squashing migrations, but certainly not without manually writing those migration files.
/Markus