When you modify Monitor I session options

Assume that the options for a currently active session include CHAN, NOCPU, and NOSTOP, and that you want to modify these options to NOCHAN, CPU, and STOP(40M).

If you issue the command:

MODIFY RMF,MODIFY ZZ,NOCHAN,CPU,STOP(40M)

the options will be modified as you want.

If, however, member ERBRMF10 includes the options:

NOCHAN
CPU
NOSTOP

and you issue the command:

MODIFY RMF,MODIFY ZZ,STOP(40M),MEMBER(10)

RMF™:

Merges the input option from the command and replaces NOSTOP in the current option list with STOP(40M).
Merges the options from ERBRMF10 with the current options list, replacing CHAN with NOCHAN, NOCPU with CPU, and STOP(40M) with NOSTOP.

Thus, any options in a member will override both any current options and any options specified on the MODIFY session command.