The 535 and 524 are completely different engines, yes, their thrust rating is different, but also their fan diameter, nacelle, engine mounts, everything really, there are no (or maybe 1 or 2 ) common parts between the 2 engines. Just like the GE90 series, where the dash number is an indication of the fan diameter (in inches) the GE90-115 has a 115 in. fan diameter (flipping big is you ask me).
Thrust bumping is common, for example the V2500-A1 and -A5 are basically the same engine with a thrust bump for the A5. The RB211-535E4 has an E4
-B and E4
-C variant, each is a thrust bump from it's previous version. The 524 is a completely different design (have I already said that??) it is not a thrust bump of the 535 just as the PW4198 is not a thrust bump of the 4094 or the GE90-115B is not a thrust bump to the GE90-90. The CFM56-7 is not a thrust bump to the CFM56-5 which is not a thrust bump to the CFM56-3, they are all different designs, different engines each deisgned for a specific airframe. Minor changes do not necessitate a engine designation change, if there is a change which affects the type certificate or operation of the engine, then I think there would need to be a designation change, otherwise minor changes should be just identified on the date plate or in the records of the engine.
Also, even the Trent Engines are officially called RB211-Trents.