I am not very sure but I think the BIOS setting is only needed if you are coming from Win 8 down to Win 7 (compatibility support module or CSM is required to downgrade to Win 7). In my case, I didn't have to do any change in BIOS settings to run Windows 8. I just popped in the hard drive and Win 8 installer. That's it. I hope someone else could verify that here. I also have an HP with UEFI disabled by default. But if you just go ahead and try, it won't harm your system in any way. Just make sure the Win 7 hard drive is disconnected.
Btw, before you start the installation, go to HP support website first and download all the drivers for your hardware compatible with Windows 8.
Link Removed