Swamprattler,
My buddy and I just went through this same thing. We were crow hunting two weeks back and he changed choke tubes. Then this past Friday, he went to change it back and it wouldn't move. We couldn't understand it, because 2 weeks ago, he put it in with just his fingers, didn't even tighten with a wrench. well, we sprayed with WD-40 and he found that a quarter fit the notches really well. I put the quarter in some vise-grips while he hel d the rifle. It was all we could do to turn it, it would turn out about 1/4 of the way then it would freeze up. we kept adding oil and WD but it still kept locking up about 1/4 of the way out. Finally we said the hell with it and we really cranked on it. We pretty much ruined that quarter, but it helped to protect the choke tube. It finally came out, with us sweating like we sprinted a mile.
I couldn't believe it, but that choke tube was rusted pretty good. Not pitted, but rust in the threads on the tube and in the barrel. We used a very fine bronze wire brush and cleaned all of the rust off of the threads. All of our choke tubes now have anti-seize on the threads.
GOOD LUCK.