I see your point, and it is valid. Most of the time, however, you can handle these things with either page 42, or the monster creation rules on-the-fly. If they suddenly punch someone you didn't think they'd punch, take 10 seconds to flip to the appropriate page, and have them do their thing.
Really, I think this is not a *huge* deal, and I'll illustrate. In our last session our PC's were trapped in this illusory bubble/time warp in the Mournlands. We had figured out that nearly every meaningful person we had interacted with in the past two months were in fact illusions. While walking through the market, my PC was approached by a seller, and in a fit of frustration, took a swing at him. The DM had me roll an attack. I hit, the seller dropped his wares and ran away.
I know that my DM did not have stats for this guy, and he didn't look anything up. He decided on the spot whether that roll was good enough, and roleplayed it accordingly. In this same 'trap' we are caught in, there are several soldiers and other dangerous baddies. If he thought the seller was dangerous, he could have thrown in the stats of a town guard and we would have had a scuffle. He didn't, because he didn't need to. It did not fit the situation. It did not further the story.
I still feel like maybe this locksmith thing is being worked at from the wrong side. *First* decide how or why he might get attacked, then decide whether it is worth it for the party to fight him. If you still need stats on it, there are several hundred appropriate stats, of all levels, in the compendium for you to steal. That is barring you taking a 2 minute break to make something up.
I see your template in the House Rules forum, and it is a nice system, but big and bloated and retro, in a we-don't-need-that kind of way. Like fins on cars, your idea is not a bad thing necessarily, but is unwarranted. Look seriously at the advice in this thread. Several very smart people (not me) have given you ways to do this in a much easier manner, and they are backed in this by much experience with the game system.
As always, this is all just opinion, and ill-worded at that. No offense taken if you do not agree.
Jay