How to do repair without losing settings

I have win 7 pro OEM installed on my custom computer. I am trying to change my ASUS P6T Sata setting in BIOS to AHCI. I Get a blue screen when I do this. According to ASUS I must reinstall Windows which is not an option since I have tons of applications installed or they said I can do a repair. Like other MS OS's there is a repair when first booting but I need to use the repair option you normally get after starting the installation when it sees you already have the OS installed. This is what ASUS said and I have done in the past with other OS's. However unless I am missing something on my WIN 7 64 bit OEM install when I start the install it sees my drives and partitions and my only option is to pick the partition to install to and it it does a full install. Am I missing something? Any other workarounds or suggestions?
Thanks

Yes, the blue screen is normal for doing that.

You don't have to re-install Windows, although that is the recommended approach.

You have to set the bios back to where it was. Reboot to Windows. Install the AHCI driver but don't reboot yet.

Then there is a registry alteration to make, so that the machine boots well using AHCI.

I'll Google for it and see what I can find. I forget it, from the top of my head.

Here ya go. This should explain it well enough:

Error message when you start a Windows 7 or Windows Vista-based computer after you change the SATA mode of the boot drive: "STOP 0x0000007B INACCESSABLE_BOOT_DEVICE"

You are the Master. I bow to you. One change in the registry and two reboots and problem solved.
Thanks !!!!!!!!