When editing the GL account structure to update a calculated using option, the system will remove all previous definitions for that part of the account number. In other words, the mapping table for that part of the account number found under General Ledger Setup, Define Segment Mappings will disappear and then that segment will need to be completely remapped.  It's recommended to exercise extreme caution before making this change and export the previous mapping table for reference as segment mappings cannot be imported.

1. Go to Financials, General Ledger Setup, Define Segment mapping
2. Select the segment that needs to be changed
3. Click the More button and Export the grid to CSV or XLSX, keep this file as a reference for the new segment table that will replace this one.
4. Go to Financials, General Ledger Setup, Define Account Structure
5. In the left-hand panel select Define composite segments
6. Add a new composite segment which contains the transaction types that need to drive the segment that is being updated.
7. Return to Financials, General Ledger Setup, Define Account Structure
8. Edit the desired account segment, and choose the new composite segment just added in the Calculated using drop-down
9. Click Yes to the message
10. Return to Financials, General Ledger Setup, Define Segment mapping and select the updated segment
11. Using the export from step 3 as a guide, enter all of the mappings for this segment.

It's strongly recommended that you enable the unmapped account setting during to this process to ensure that other users of the system are not disrupted while the GL configuration is being changed.