Yeah, could understand the reasoning behind wanting to make it do something. Just think it actually debuffing you makes choosing one you like instead of one you want for the character an issue. The kind buff, for example, I liked. Made sense, gives you slight buff that may not affect character its on, but if it doesn't, oh well. Doesn't hurt you not having the buff. Whereas an actual debuff can actually hurt the character. Since shy raises matk, can understand wanting to lower atk as a counter, but wondering if it may not be better choice to just lower the bonus and remove the debuff instead, because then its more like the kind one. That way having a certain personality CAN help slightly, but it doesn't cause problems if you want a different one.
As for modding it, I've no idea how to mod this game. I can install mods, but not make them. Only seems easy if you know coding. Unless you mean using json editor on save file to alter bonuses? That at least I know :D