Assume I have a campaign that I've already saved at least once.
What changes can I make to the mission file "midcampaign" that will actually stick once I load up my saved data again?
Can I blacklist taors?
Can I tweak what types of reinforcements are available?
Need to know what mission makers can and can't tweak in their campaigns without having to restart persistence from scratch,
That rather depends on what you have chosen to persist . For example, if you do not persist the AI Commander, you will be able to change the objectives (TAORs/Blacklists) and he'll 'reset' the decision cycle. As long as the Virtual AI are persisted, the Comd will pick up whatever he has available and start from there.
You can change logistics blacklists no probs - only the available forcepool is persisted (assuming you have it set to persist)