Can't find my old reference material on this so I'll post the question:
If a lead lender sells a loan participation but retains the right to buy back all or a part of the participation, does that change the accounting or regulatory treatment of the participation? (I know it does not change the non-recourse nature.)

Not to my knowledge.
(If it does, then I've messed up more than one participation. )

No, it does not change the treatment. You may have an issue, however, if the right to buy back does not specifically exclude delinquency, etc as a triggering event.

Well, I found the old info and the answer is in FAS 140. Retention of an option to repurchase is a no-no.