I don't change things one way or another for any PC. If it makes sense for there to be a cliff, there will be a cliff.Again the DM controls the fantasy. In a world where centaurs can be adventurers and adventurers need to climb ladders, either some version of equipment will exist to enable it, or the centaur can just do it. EZPZ.
It's all imaginary; the only things that are physically impossible, are the things the DM decides are physically impossible.
Also, this is not to say that centaurs should have zero issues. IIRC, they are still large creatures and so subject to the same mechanical issues other large creatures run into. Anything beyond that is just fiat.
The world does not change for any PC and a centaur could not climb a cliff.