Control over these is tied to a more constrained IC system basically to make players deal with dice rolls and to stop them from fiddling with them obsessively which is roll-for-everything game design I don't really agree with, but for minor adjustments that reasonably would fall within a character's short descriptor (average, hulking, etc) I see no issue myself with making small descriptive changes as characters gradually fill or waste away, without bringing the Torment Nexus of game design (ie. biomods) into it.
If there's a player who has been through chargen a few times recently and knows how everything maps out they could post that information and I can write some help files, or they could do it with @new-help.