Well--I know what chords and rhythm are; not sure I understand your question. Maybe more explanation: I am developing this as a trio backing for practice. Trio being a rhythm section of bass, drums, and acoustic piano, over which i will play melody and improvise in a standard bop style. The tune is 32 bars. I will play through it 6 times. On the first time, I want bass, drums, and piano to play only on the the downbeat of bar 31. I want them to rest after that and to resume 7 beats later, on the downbeat of bar 1 (2nd time thru).

I've been to "edit settings for current bar" multiple times even before posting this question. At least in the view I have, there is nothing called "mutes" or lower volumes, and no place to specify chorus. I am on BIAB from mid 2007, if that matters. All I have are the following
-# beats in this bar
-temp change to
% change in temp
patch changes in this bar (separate menus for bass, pno, drms, guit, strng, melody, soloist, thru
Harmony changes at this barmelody harmony--at beat #
thru harmny--at beat #
reset bar
reseat all bars
ok
cancel
help

That's it. No mute, no volume settings, etc.