I'm not sure charactermancer is the problem. If your players are abusing your trust, there's far worse they can do with manual editing of their sheets. A player could change the base die of their weapons, memorize spells not on their list, etc. There's no way you can stop someone determined to cheat, other than to boot them out when you catch them. If you want to have total control, have them tell you what they want from their character. Make the changes yourself. Give them control of the character, but not the ability to edit. But that sounds like a nightmarish way to run a railroad.