-edit- added missing step 3, otherwise it will complain of 2 device with same mac address
Try the following:
1) go to manage page for the controller that's showing wrong model
2) set IP to something else that won't respond to SNMP
3) in the db, set the lan_mac address to something different as well (this step is required in order to fake out the database for the replacement)
# dbc "update ap set lan_mac = '00:0B:86:11:11:11' where id=<ap_id>"
ap_id is gotten from existing controller entry's URL
4) go to device setup -> add
5) add the controller again (with correct IP)
6) confirm that it comes up with correct model
7) then go to the original controller entry (it should be reporting down by now) and do replace hardware, selecting the newer good controller entry as the replacement
This should keep historical data attached to the controller entry.