What would be the logical reason why high psi capability soldiers should not be able to get this enhancement? At least usually high PSI is "something extra", not something that blocks or prevents other progress or makes you weaker?
Of course I can imagine scenarios how this could maybe make sense in other settings. For example, consider a "rookie bootcamp" transformation/training, which could only be applied to relatively fresh recruits, and which would essentially just provide a boost to some stats. Then it would make sense that the veterans would not want to go there and would maybe not even be admitted in such a training. Not sure how interesting something like this would be for modders though, and there could be problems how you define the various limit(s).
