I'm trying to make basic recordings for a few of my younger students to learn 8-6-7 with crescendos. I've been having amazing luck giving them mp3 files "missing" a particular voice (snare, bass 3 etc) and I've so far been totally useless at figuring out how to incorporate different time signatures while transposing out of the "fresh Persectives" book (considered the kids "holy bible of chopitutde" to quote one of them lol).
If there is a simple way to do this I'd love to know it.

Changing time signatures? Click on the measure and type "T"

When I do that it changes the entire battery's time signature. I'm looking for a way to have each instrument have a different time sig (snares have 8/8, tenors have 7/8, basses have 6/8 all at the same time). Couldn't find anything on sibelius remotely close.

This is a very non-standard way of writing, so it's not all that common to do it. Read through the FREE RHYTHM and TIME SIGNATURE sections of your sibelius reference manual and it'll walk you through the process. You'll have to create irregular bars, and look up the 'multiple time signatures' topics.

ah ha! Thanks Jim, I don't know why I didn't think to look for Free rhythm. This will be a big help considering I'm in the middle of arranging Pictures at an Exhibition for next spring's marching season.