I think modding is best when done with stuff that is modular. For example: drums. Heads, rims, sticks, tuning, resonant sides, dampening rings, etc. There are a LOT of things you can do to your drums to change the sound without damaging the shells. You might have to replace a few heads here and there, but the drums should be fine, and each of these small changes will make a change in how the drum sounds.
And heck, this sounds a lot like tube rolling. Different tubes may or may not result in an audible change, but for rollable amps, it offers a cheap(ish), quick, and easy way to make a change, and after rolling to different tubes shouldn't damage your amp (unless you do something very, very stupid).
The most interesting modding community has to be in PC gaming, though. Here, you have mods that revive older games, mods that overhaul core systems, mods that upgrade or replace textures, and on top of all of that, some huge games started out as mods (DOTA, Team Fortress, Counter-Strike). I can't say I've dabbled too much in this community, but I am very glad it exists.