Of course you can change the button mappings to whatever you want to; however that only changes the OS interpretion of the buttonset, it does not affect things like long-press-to-hard-reset which is wired on the chipset and power&volup to enter boot selection which is determined by bootloader.

And BTW just call it an OS image instead of a "ROM"...
It is such an android-centric ugly word which does not really mean what it's supposed to.
It's as wrong as using word "hacker" to mean a blackhat.