Does the MBoard/CPU knows if the HD was previously formated? I guess is like a PC, it doens't know.

So if you change the HD, just like a PC, it should work with the new SO, or whatever is inside the HD. You only need (?) to setup the HD, like in PC BIOS. ??

In PC if you replace the HD with other SO prepared for a different hardware, the SO will work anyway, it could have some problems/conpatibilities with the new hardware, but it will work...
In PS3 the hardware is allways the same ... only the size of HD is different... so it should work... (?)