Thanks Sylvia. I received a reply from Asus tech support saying I DO have to reinstall Windows 7.
Actually after some more research I suspect both answers may be partly right. My *guess* is that switching from the RST-E OROM to the RST OROM probably means that my existing RAID-1 boot array will no longer be recognized. It will have to be recreated under RST, meaning loss of all data.
Anyway my plan is to temporarily clone the existing boot drive to an HDD hanging off the Marvell SATA controller on the board. Then I can boot from Marvell, and change the drivers for the now-unused Intel controller. Then re-create the RAID array under RST and clone from the temporary HDD back to the new array.
Maybe I'm making extra work for myself, but at least I'm fairly sure this will work.