I highly agree with being able to reset your charm multiple times til you have the one you want, I think that genins should be able to do it aswell though, as it might affect your performance in fights to some extent, but just for them it being a bit more pricey like 2k or 3k.
I just feel like charms as in buffs should not really be rng, especially when f.e. a water/earth gets an agility charm, they get a buff for literally nothing, while others might get a better one and can do more, in a close fight those small buffs might end up relevant.