I'm not sure what your rather cryptic post intends, but here's what I think you're asking
Q: When you use a different train with a given coaster, do the coaster's or the train's restrictions/features control?
A: From what I can tell, it's always been that changing the train is merely a cosmetic difference--the coaster is always what it was when you 1st placed the station. It keeps calling itself by the default name of the coaster even after you change trains. Therefore, the initial choice of the coaster to start with determines what track pieces are available and their minimum sizes, whether inversions are allowed, whether or not the coaster allows kids, and even the lateral spacing between the catwalks and the track. The only actual difference changing the train makes is that it might reconfigure the cattle chutes of the station to match the rows of seats on the new train.
I have not heard this has changed, nor have I seen any evidence that it has.