I recently bought a SSD and enabled AHCI mode before I installed the OS on it, I changed the registry beforehand but on the old HDD's OS and so I thought it was all good but only after I installed the new OS on the SSD I found out I actually enabled AHCI for "RAID Mode" while the real option was under "On chip ATA devices > RAID Mode > AHCI" and only then did it installed all the drivers. My question is should I expect problems? I didn't had any BSOD afterwards thankfully so maybe the first option I enabled did work in someway.
If you did the registry changes correctly, you should be OK. What you are trying to change is the SATA mode from IDE to AHCI/AHCI RAID Mode. I'm not sure what your BIOS is, so I can't say for sure what you mean exactly. But if the drives both function as expected and the SSD boots to Windows, it is working.
Did you do a clean install of Win7 to the SSD, or did you clone the HDD to the SSD?
If you were clean installing Win7 to the new SSD, you didn't need to make any registry changes for AHCI mode. The old registry is history now that you have a clean Win7 install. What MB is it you are using?
I didn't made the changes on the SSD, I did it before I installed the OS (on the HDD). I do however still alternating between the drives until everything is settled on the SSD (and I do plan to keep the HDD as storage). My MB is MSI P55-GD55.
I just downloaded your MB manual and checked the SATA mode section. RAID Mode in either section you choose is the same thing. It just appears in both places. If you change one and save, the other should be changed too. So...
If you went and changed one back after changing the other, the last one you changed will be in effect.
Well I can tell you for certain that the other one was not changed too and was still on IDE mode and only after I changed it to AHCI and reverted the other one to IDE (since all it did was show up a JMicron screen that took a couple of seconds every boot) it installed the drivers that it should properly.