Does a pilot follow the PAPI lights in the same way in all categories of aircraft?
The lights themselves are fixed, there is no way ATC or the airport operator can simply adjust them to suit the next inbound aircraft. If the pilot needs to they can fly the approach with 3 whites/1 red, but AFAIK that isnt really necessary in most situations (maybe for 747s and other longer aircraft). 

It's worth remembering that the PAPI cannot provide precision to the foot. Having 2 white lights only means you are anywhere between about 2.8 to 3.2 degrees on a standard approach, which can be a considerable range when you're a few miles out.