I think you should think about a couple of things…
- Where are they in the review?
- Will this meaningfully change your application?
So yes, you can send another update and they can add it to your file. They may have read the file or not, and while it sounds like an exciting award to have won – congratulations! – you now need to ask if it’s of the type that changes your file.
Personally, I would not send at this point, go to States, and if I ended up on a WL, send the results of States to that school when explaining why I would enroll if offered a place.
If you feel this is truly a game changer and want to send, do it and note that you realize it’s late in the process. I can certain see how for an athletic recruit, achieving a certain time could be important info for a coach.
I’m guessing you have already demonstrated proficiency in the area in which you won this prize and it makes you eligible for a bigger prize which you are now competing for but it’s not going to meaningfully impact your application.