You can do this by F5 key.
For example, if you want to mute at bar 9 for 8 bars.

At bar 9, you press F5 and select mute. The song will be mued from that point on (for the inst that you select, or all instruments)
At bar 17, you press F5 and select "normal", which ends the mute.,

The song will be muted from 9-17 (8 bars).
================================
Alternatviely, you can also do this by using rests. For example, if you want to mute all but drums and bass, and it is a C chord, you type C.db (rest, except drums and bass).
Then choose edit-copy rests, and this will copy the ".bd" part to all chords in a range (for example 8 bars). Then those instruments will rest (mute) for 8 bars.

Have Fun!
Peter Gannon
PG Music Inc.