An old-school Fuji film canister is the correct diamter to slip over the head of a 501b IIRC... They are the translucent white canisters, and make a fairly decent budget diffuser if you have one laying around. I treasure my old film canisters...
For some much larger lights cutting the top off of a 1/2 gallon plastic milk jug to the right diameter works as a good diffuser taped onto the light front. Fenix makes a shallow cup shaped diffuser that works with their TK50 and TK60 For indoor lantern use you want a dome shaped diffuser so that you get light to the sides as well as out the front.
Most zoomies have sliding heads that can be removed, usually by unscrewing the pill, taking the head off it and screwing it back in. That gives a bare led that illuminates about a half sphere or a little less. You can put that under some sort of diffuser or under a regular lamp shade to get soft general lighting.
I don’t see any safety hazards unless the battery is badly abused or very poor quality.