I think jevil and sans are meant to represent two sides of narcissism. Sans's Point of view is "nothing matters, so why bother?" While jevil's is "nothing matters, so I can do anything I want!!"
This implies that jevil says he can do anything but means he can do anything he wants without the consequences. If he could canonically do anything, he could just escape the prison he was trapped him instead of convincing kris to find the key fragments.