If, during a tournament, a player reaches a rating or level which would have disqualified them from entering it, he should be allowed to withdraw either immediately, or when he has finished his current round.
I'm sure some highly rated players value their list of much lower rated tourney wins, but under the current system players who might feel embarrassed by beating much weaker opponents can't withdraw after the tourney has started. If a player wins his round (or comes second in some cases), he's automatically entered into the next one.
As all tournament games are rated, there would be a ratings dive if s/he resigned games during the round. Also those games would be recorded as losses in that player's game history.
A withdrawal option could allow a player to finish their existing games, but they wouldn't proceed to the next round. The second and/or third placed players would proceed in that case.