The magazine tube is a semi-permanate installation at the factory. Meaning alot of some type locking goop on the threads. They want it returned to them for service I guess.
That being said, I have changed out one in the last 20 years. It's possible but being as careful as you can you'll probably mess up the tube. I used some heat and when it finally broke loose was still tight unscrewing.
If you know someone with a lathe, chuck it and apply heat to receiver. Unscrewing receiver from tube instead of the other way around.
May I ask why you need to take the magazine tube off?
The Benelli M4 is one fine shotgun out of thr box.