Didn't work out so great for two guys in Kansas. Kansas passed a very similar law several years ago. They were convicted, and even filed an appeal to a higher court, and the higher court upheld the conviction.
Gotta use Texas' law as written before you jump into the "Fuckthefeds, grab the pipe cutter!" mode and get the AG to seek declaratory judgement for you.
That's what differentiates Texas law from the others - while well intentioned and pushing state's rights, and cutting the feds off at the knees since their power is derived from the commerce clause (no interstate travel / commerce, the feds need to pound sand) - our law has the provision to get the AG to go to the fedgoon courts and seek relief from the NFA on your behalf.