Can returns (credit memos) reference the new tax regime rather than the old tax regime?

We are in the process of moving from an old, upgraded 11i Tax Regime to new tax regimes, using R12 Tax Rules. All new transactions (orders, invoices) have the new tax regime, however returns (credit memos) reference the old tax regime that was in use when the original order (and invoice) were created. Is there a way to have all returns and credit memos for old orders reference the new tax regimes?

From a reporting perspective, it means we still have to run tax reports against the old regimes. It also means that we cannot disable old Tax Rates.

Any advice greatly appreciated. Thank you.