so hey basicly im new to the modding scene and i decided to use a different type of screen than the psone screen and it will use seperate power than the n64. if i were to use the two cannon bp-911 batteries to power the console alone (using the step down regulator as well) would the 4 amps damage the n64?
Amps don't "damage" a system. The system and screen will only pull the current needed to run it. For an N64 and a screen that is around 1A. So your 4A batteries would run your N64 and screen for around 4 hours safely.