Although my previous post said you should not configure the 6800ia independently, it is possible and should be done at least in this case.
Here is how it’s done:
(1) attach to fex using (attach fex-id <>)
(2) Go to config mode and run the below command:
Switch(config)#switch 1 renumber X <== Do this for every switch in the stack
(3) save the changes and then reload the stack members
this worked fine for me although when trying to save the changes I got the message “NVRAM Verification Failed”. On reload the switch’s number had changed successfully