SBR7_11: Agreed - this is one that needs a sticky at the top of the forum.
MartyW:
1. Blind pin and weld over the pin, or high temp (1100F) silver solder, or seam weld at least halfway around the brake.
If there's no flash suppressor made for a particular thread, it doesn't have to be covered, but that would mean getting a custom brake and custom threading job. I'd recommend and oddbal like 1/2-40 or even an odd pitch if you want to go that route. If it's a standard 1/2-28 or 1/2-36 or such, then the brake needs to be permanent to cover up the threads.
2. It's true, no clue what they're really up to, except banning all guns bit by bit.
3. Yes, provided no flash suppressor exists to fit those threads. Whether the threads are internal or external doesn't matter, as long as there are no flash suppressors for it, it'd be legal. However, it would be a pain in the ass custom job to have a special inside threaded barrel and outside threaded brake.