Can I wear my dress uniform in a veteran's day parade and preform?

I wouldn’t. It would come off as an ‘attention grabber’ thing. Not to mention you aren’t in that organization as a Soldier but as a student. But that’s just my opinion.
There are MANY things we ‘can do’ but that doesn’t negate what we SHOULD DO.

You are in a band, which has its own colors and uniform. You would look out of place in the parade wearing your dress uniform while they all wore something different. You could but but really should you? It's one thing if there was a military portion of the parade and you were marching alongside other soldiers, airmen, sailors or marines but this is not the case.

Show up, in your school band uniform, march and play.

If you are marching with your HS band, you should wear the same uniform as them, show solidarity. It is refreshing that you are proud of your uniform and accomplishment, but trust me, there will be other, more appropriate times to wear your service uniform.