Many clients request that corrections do appear negative on the respective debit or credit (amount) side.

This is accomplished with the Correction flag (either in the journal line or the document header).

Now, if a company chooses to have e.g., sales invoice account and credit memo sales account to be different in the general posting setup, the account to be used when posting the corrective sales credit memo should not be determined by the general posting setup blindly, but it should of course use the revenue account from the original invoice.