Unless RMAN tells NetBackup which policy and schedule combination to use, the master server will pick one for you, and in your case it sounds like that's happening, and not picking the policy/schedule combination you want.
So in the actual RMAN command you can add the SEND statement, it goes inbetween the ALLOCATE CHANNEL and BACKUP statements.
The SEND statement should look like:
So let's say we want to backup to the policy called OracleServers, and to the application backup schedule called EndOfMonth, your SEND statement would look like:
So that's handy, but now you're asking yourself how do I do this all from the same script, well you've got to add some logic to your scripts, and then change around those values inside of the SEND statement. When NetBackup kicks off an Oracle type backup from the scheduler, or from a manually initiated backup from the NetBackup Administration Console some variables are passed to your script. The most valuable variables are NB_ORA_POLICY, and NB_ORA_PC_SCHED. NB_ORA_POLICY is passed with the name of the policy which has been run, and NB_ORA_PC_SCHED is passed the name of the Automatic schedule. Seemingly based upon the names of the policy and schedule starting the backups you could then configure the NB_ORA_POLICY, and NB_ORA_SCHED values in the SEND statement.