The warning nobody reads

The documentation says you can review and update the setup before users start using the application, and once there are transactions these setups cannot be changed. That sentence is the whole module. What "cannot be changed" means in practice, the recovery path if you get it wrong — a new cost organization and a data migration, which on a live plant means a period end, a full revaluation and a conversation with the auditors — and the sequencing consequence: nobody transacts in a new organization until the costing design is signed.