"...the invader will be shown to have been lethally armed by the time the cops show up, whether he was at the time of entry or not..."

Sounds nice, but get caught doing that (they are getting better and better at detecting that very thing) and you will suddenly go from the innocent guy defending himself to a bad buy trying to cover up his crime. It is a variation of the old saying, "once a lier always a lier"...