You can change the setting of the Allow shared branch trans field on the member's master record.  When that member's account is selected at one of your shared branch locations, CU*BASE will display a message that shared branch services are not available to that member. (Make sure all your shared branch partners understand what to do when their tellers encounter this message!)
To update this setting, use Tool #15 "Update Membership Information."  (The flag appears on the final update screen.)
NOTE:  This flag controls access via both CU*BASE Shared Branching and COOP National Shared Branching tools. For national shared branching only you can also configure a setting to prevent new members from using shared branching for a period just after a new membership is opened. (This is configured as part of the COOP Shared Branch Issuer Configuration daily limits settings (OPER Tool #5432 > Add Limits).).