Stupid
Did these geniuses never think that a school might actually notice when someones grades shot up overnight? Even setting aside their horribly botched means of tampering with their GPA, unis do keep paper records of these things and one would think registrars are smart enough to do a little digging when someone at the bottom of the class rankings suddenly rises to the top. Even if the tampering went undetected due to failure at every level of responsibility solving the matter would take about a minute (plus ten hours scheduling time judging by standard uni efficiency):
Reg: So, how did Mr. Jacquette do last term? Good student?
Prof: Oh him, never attended classes, got one question right on the final. I think he was drunk at the time.
Reg: Thank you.
Of course, if these students truly were getting a lot of Fs then perhaps they're too dumb to realize that, though it also makes one wonder why they weren't punted for academic underperformance before they had a chance to act out their script kiddie fantasies.