It should be possible through zman or preferably ZCC to fully automate the creation of bundle and policy to user assignments in case of a user source change. We have many customers who are migrating from eDir to AD and right now it's really painful to migrate all of the (eDir) user assigned bundles and policies to the new AD user objects.

Since most of the time the user objects in the new user source got migrated using IDM and thus are named equally it should be possible via SQL to match the assigments to the new user objects.