You can only edit a reporting unit code if it is not used in General Ledger Manager. You can always edit the name and notes associated with a reporting unit code though. Any corresponding units or entities that were created for a reporting unit, however, must be edited in their own applications.
Note: A reporting unit code is used in General Ledger Manager when it is either (1) present in at least one imported trial balance in Review Trial Balances; or, (2) present in a reporting unit exception in an account map; or, (3) mapped to an entity in reporting unit rollup.