[officialtony]

Ric, I'm not sure there is a " right " call, but I'll try.
Your terminology has me confused on this one. If it was " after the match ends " but before the offended wrestler leaves the mat area, then there are some things to be considered. If Wrestler A was eligible to compete at 125 ( having legally weighed in for that weight class ), then the match is valid, despite what the coach from A might say. If he wanted him at 130, it was HIS responsibility to know when the 125's and 130's were wrestling. If he was not eligible ( see above ), then A would actually be disqualified, and B would receive 6 team points for the DQ and not 3 for the decision. AND . . . . Team A would lose a team point for the subsequent UC that should be assessed to the coach by sending out an improper ( illegal ) wrestler to compete. I believe that is the " by the book " ruling on this scenario. If you, as an official wanted to call it bad time because the table ( or you ) allowed this to occur, then the entire match could be ruled invalid and you could allow the proper match to take place - after a minute rest. That might be a stretch of the rule and you would have to eat this one, assuming the responsibility for the error. I believe that is the only way you could allow A to rewrestle. And then . . . . you are going to have to listen to the coach of B go on about how it is wrong. AND . . . . . . this must all occur before the next match begins ( 130?). If the next match has started - nope, sorry coach, too late.
However, if it is after the Dual Meet ends and before 30 minutes has passed, that this is discovered, there can be no rewrestling of the match. You can, however, change the team score to reflect a DQ from the above scenario, if A had not competed legally at 125 ( if he was not weighed in for 125 legally ). If A was legal, then there is no change and no rewrestling. Sorry coach. Shame on you for not being involved in the meet.
Finally, if it is more than 30 minutes after the Dual Meet has ended, NO changes can be made for anything.
Didn't want to make this too confusing, but there were many things to consider.
If you have any questions, I'll try to expand on a certain area for you.