The SAVLIBBRM command just piggy backs off the OS SAVLIB command so you can expect to have similiar parms.
Prompt the SAVLIBBRM cmd, press F9 for all parms, scroll down twice and you will see the Libraries to omit OMITLIB parm. Enter your values here.
I assume you are using BRMS control groups to do your Backup. You can exclude libraries from *ALLUSR doing the following: WRKPCYBRM *BKU. This will display a littel menu where option 2. Work with items to omit from backup is the thing you wan tto look into.
You can exclude libraries from *ALLUSR, *ALLPROD and so on (check help text).
You can run your BRMS control groups (STRBKUBRM) with processing these omits, or without. (PROCES parameter on command).