I am going to be a freshman in high school next year, and this year I auditioned for the highest level of band the high school offers. I made it in. I plan on switching instruments and playing horn next year, instead of tenor sax which I currently play. I know of kids who switch instruments while in wind ensemble(the highest band level), but would it be wise to continue in wind ensemble playing a new instrument? Or should I switch and drop down a band level? I'm so conflicted, advice?
I can't tell you what you should or should not do, but...
I would drop down to the middle/bottom band, personally. It'll be a lot easier for you to learn the instrument and straining to do things you can't do yet can cause you to have terrible habits, and probably will.
If you're good enough to have gotten into the top band this year, work hard for the year and re-audition for the top band the following year.
However, if I really was in your situation I would stay on your tenor for this year and play with the top band once, learning horn on the side, in order to ease you into your new high school atmosphere as well as it being a great learning experience. Then, I would audition with horn the next year and see where it puts you.
In the end, it's up to you!