Default Question about S voice

So currently I have voice wakeup control on. I was wondering if there are any custom ROMs that replaces the S voice app with google voice control app completely? I know I can use S for Switch Voice app, but that's battery and resource intensive. Also, how come we are restricted to saying hi galaxy to wakeup the device> can't we change this like some of the other phones? any custom Roms that does this as well?