I don't have a CM in front of me, but I think I can get close enough for you to make your change:
+ use the Web interface to the S8720
+ login
+ use the Maintenance link
+ there are two snmp buttons (snmp agent and snmp traps), choose "snmp-traps"
+ change "master agent status" to "down"
+ click "version 1" (unclick "version 2c")
+ change/add ip address of trap receiver if necessary
+ change "master agent status" to "up"
done
steve