I hope this posted in the legal section!
Question: I have a preban upper. I have cut off the bayo lug(one evil part gone). Next can I screw on some sort of muzzle break(not supressor) and then weld it. would this be legal? Technicaly the threads are sill there, just cant use them?

Yes, welded is OK.  So is high-temperature solder.  I like the way ArmaLite does it - They drill a blind hole that cuts into the barrel, drive in a pin, then weld the hole closed and grind it smooth.

The brake (not "break" BTW) cannot be 22 mm in diameter like a standard military muzzle device 'cause that's a standard size for Grenade Launchers of Doom.  BATF has approved specific kinds for use on post-bans.  See your friendly parts supplier for details.