Would hiring an agent make him ineligible for collegiate athletics? And then making him draft eligible, three years after high school?
He'll be draft eligible 3 years after high school no matter what, so yes. While the rules do say players who have yet to exhaust their college eligibility must apply for draft eligibility, I don't think anyone has ever been denied, so as long as he waits 3 years from his HS class graduating (technically the player does not have to graduate), he can then be drafted.
NFL has undrafted free agents. With today’s structure, and the fact that they don’t play American football for real anywhere else, it’s just uncharterted territory to give an undrafted FA a newsworthy contract way more the more than minimum, or having teams fight over a UDFA.
Undrafted free agents are all guys who were draft eligible just not chosen. Lawrence would be draft eligible 3 years after his HS (so for the 2021 draft), and presumably would be taken in that draft whether he plays the next two years for Clemson or for the XFL Fingerblasters or whatever ridiculous team names they come up with this time.