[fwip]

I feel like if you're modifying the signature after they sign it and approve it - that could be a problem. As long as the modifications are applied in real-time (or with explicit user confirmation after modification), I think it is morally okay (and probably legally, but I'm not a lawyer).

You may find users who get mad if your settings are too aggressive though, and if they're unable to get a signature that they approve of.