I want to get my tongue pierced this Friday, but I don't know if I can because I play a brass instrument in a wind ensemble and we practice twice a week. If I were to get my tongue pierced Friday evening, would I be able to play my instrument on Tuesday?

No... definitely not. Your tongue can be swollen for up to 1.5 weeks so playing a brass instrument is out of the question. Not only will it may not sound that great, but you could also cause trauma to your tongue. When you get a piercing, you are causing injury to your tongue, an open wound, and that wound needs time to heal. I suggest that you hold off on the tongue piercing until you are done with band.

I know how it is, I play the clarinet, and there was no way possible I could play it so soon after getting my tongue pierced. I would suggest to hold off on the piercing if playing an instrument is important to you.