To change the rollup for an account in BPC do the following:
- Change PARENTH1 on the account to the new rollup
- Process the dimension (Do a Full Process)
- Make the Application available
- Click on the Noble node
- Click on Set application set status
- Select Available
- Click Update application set status
- Refresh dimension members on the client.
- eTools -> Refresh Dimension Members
This will probably work for any dimension, not just accounts.