Newer versions of the robot have an 'expert-mode' controller callback which can be used to reset the robot device id and restart the robot (thus resetting them to unique values).
To use this callback (assuming you're running on robot 5.70 or newer), use the following procedure:
1) Navigate to the robot which needs to have its device id reset
2) Highlight the 'controller' probe and hit 'CTRL + P'
3) When the probe utitity for the controller probe comes up, select 'Options' (the thumbnail with the gear icon)
4) Check 'Expert Mode' and click OK
5) Pulldown on the 'Probe commandset' menu and select '_reset_device_id_and_restart' This will flush the niscache folder, including the robot device id. Then the robot will restart and immediately begin to repopulate the niscache (beginning with the robot device id). Repeat this procedure on all robots which were cloned (without a nicache flush).