no difference if above 55 & FRS already met. they will be refunded back.
Yes, if OA dollars (plus accrued interest) haven't already been repaid. Ghostrider's proposition is whether it makes sense to do this (for example):
1. Just before your 55th birthday, "shield" SA.
2. Fund your Retirement Account to the Full Retirement Sum (or beyond) on your 55th birthday using OA dollars and/or cash.
3. While SA is still shielded, withdraw remaining OA dollars.
4. While SA is still shielded, repay OA dollars used for housing (plus accrued interest).
5. While SA is still shielded, withdraw the OA dollars.
6. Release the SA shield.
And yes, it appears that you can do all that per today's CPF rules. If you do that then when you sell your home there won't be any OA dollars that are repaid because you've already paid them back. You get all the net sales proceeds from your home in cash. But the disadvantage is that you've destroyed your ability to repay OA, so you no longer have the option to inject dollars in that particular way into CPF where they can earn at least 2.5% interest.
Of course you could do something anywhere in between. If for example you owe $250K to your OA and want to repay $125K to yourself (to your OA), you can.