Question for the wiring/electrical nerds.

Cutting all the power wires would be safer than cutting the grounds. But - it would be a big job.

Even though it's possible to do what the OP want's. It isn't really practical. If you cut the grounds at the bonding locations, you get undesirable results by loosing other electrical components not intended to loose. If you start rerouting every lighting circuit through a relay, your going to have one hell of a lot of wires to contend with.