Field help (MERCPTORG) 

Account to merge.
If the source account is a matchable account with the matching codes A, B, and the destination account is also a matchable account with the matching codes A, B and C, the merge also merges the matching codes. That is, the As are grouped and the Bs are grouped.
If the source account is a matchable account with existing matches and the destination account is a non matchable account, the merge saves the matching codes Note: A matchable account with existing matches can be set to non matchable by clearing the check box.

When the Partner or Flow management is different in the Source and Target accounts, you receive a blocking message for the following conditions:

Source account setting

Target account result

Flowmanagement is Mandatory or Optional.

Flowmanagement is Not entered.

Flowmanagement is Not entered or Optional.

Flow management is Manditory.

Partnermanagement is Mandatory or Optional.

Partner management Not entered.

Partnermanagement is Not entered or Optional.

Partner management is Mandatory.

SEEINFOThis control is in effect only if the Chart of Accounts is associated with at least one consolidated ledger for the company.

SEEWARNINGRead the documentation for Partner initialization and Flow initialization.