Most of the nuts came out with minimal force, but the last one just spins in place. I tried rubber gloves, painter's tape, and duct tape to get a better grip. I'd rather not cut a slot in the domed nut if there's another good strategy.
The rest of the restoration underway:
It looks like the bolt is perhaps brass? I'm wondering if you can't sand the surface a bit and low-temp solder a nut or something to it to get a better grip. Once you get it off, unsolder it and clean up the leftovers.
Either way, the question I would be asking myself is: is this a tool or a decoration? If it's a tool, it doesn't seem to me like it makes sense to try to preserve the bolt. I'm guessing this is old, and if so, people from long ago would have used whatever bolts and screws they had handy to repair things; you'd be keeping in that spirit by doing the same!
I think you're the only other fucker in this thread who may have used their hands before