The tire pressure may not change (not sure I understand that theory) but the footprint of the tire certainly does! so higher pressure on the rear with no load will wearout the center of the tire, and the reverse is true too low and the outter edges will wear. sooo on an unloaded truck with 50 front 70 rear you gonna have issues.
A few years ago, I was on a course the Military ran for its Vehicle Techs. They had a Michelin Tech come and explain theory on Military tire stuff, (all Canadian Military pattern Veh have Michelin tires)any way he explained that they found fuel tsp trucks were having braking issues mostly when they were empty,(meaning they could not stop) the drivers are susposed to inflate/deflate depending on load, but one one does,and it was not practical so what fuel companys do now is when the truck leaves the refinery with a full load. it goes to its further most delivery first then it drops fuel at different stations along his route. this way by the time the truck gets back to the refinery it has travelled the shortest distance while it was empty. he had a couple of photo's of tire footprints empty and loaded with the same pressure, the empty footprint was smaller than the size of a hockey puck, while loaded was 4-5 times larger, next time you see a semi locking/smoking his tires when he brakes, you can bet his truck is empty