Does this mean that Trump is disqualified and the Democratic nominee wins by default? Or is there any punishment for violating the rules/laws/regulations like this?
My guess is that it would just be a big fine (and unlike with Clinton, the Republican appointees on the FEC board might decide they hate Trump enough to actually issue a penalty).
But even if Trump were disqualified (at this point), it's likely the Republican Convention rules committee would make his delegates unbound, and then who knows where the nomination goes. Cruz, probably, unless there's a big behind-the-scenes push to give it to Rubio or Bush.
If Trump were declared ineligible after the convention, I don't know how that would affect things. Possibly he would still appear on the ballots and his running mate would be sworn in as President, and then choose a new Vice-President pursuant to the Twenty-Fifth Amendment. Or perhaps his ticket would be taken off entirely in some states, which would probably lead candidates like Gov. Johnson and Dr. Stein to make big pushes for people who would have voted for him there.