which ones are you taking off and putting on?
Most of them do not require special tooling, but some do *cough* knights armament *cough*
If he is swapping out to a rail that attaches with a proprietary barrel nut like several out there (Midwest Industries, Odin Works, etc) the existing barrel nut has to be removed along with the gas system, new barrel nut installed and re-torqued, gas system reinstalled and rail installed. Not hard with a vise and vise block for the upper and a torque wrench, and the correct tool for the barrel nut, but those tools are quite helpful/required.