As long as it's not a return trip they won't hunt you down like the one-armed man because you left in Panama. If you do this all the time they will take issue.
If it is a round trip the CUN-PTY-LIM flight will be cancelled.
What limitations could there be to get off a plane landing in Panama and entering Panama? That's what 25% of every person there must be doing.
This sort of thing is why two one way award redemptions (assuming there's no additional cost) makes more sense. Like on AA.