Well you are very correct in your concerns about breaking or twisting the tail pipe.
I would grap the tail pipe with a vice grip that has leather or something around its jaws to protect the pipe.
Then with another wrench I would do some tugs on the head. If that does not work, use penetrating oil or WD-40 to work into the threads.
If this does not work, then get a small propane tourch and apply some heat the the threads of the shower head. Do not get the tail pipe too hot as it will melt the fitings in that section.
Just alittle heat at a time.
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