I have used the trailers hydraulic system to lift the trailer and change the tires. They used to say that you could do it, but than quit. Theories are that the legal eagles put a stop to it. I also use it to lift the trailer when I lube the axles. Have done it several times and haven't had any problems.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL