You have taken away a privilege because your teen’s behavior was poor (to say the least). You know this will cross over into a very unique event they don’t want to miss. Do you end the discipline early?
As hard as it might be unless there is some unique display of apology for the behavior, hold the discipline for the time that was stated. You want to be consistent in discipline. This is the only way it will work. Removing it because you feel bad they will miss a party, trip or other opportunity only lets them know they can get off the hook with enough begging. It also misses the point. You want your teen to feel bad about their behavior. So why do you feel bad about the discipline?
Consistent parenting is the goal. This is what allows your teen to know you mean business and it is what lets them know to avoid the behavior next time if they really want to go to that party, trip or have that opportunity. The lesson should be to change their behavior that caused the discipline not the length of the discipline that resulted from their behavior.