Dear Aaron,
The mentioned "amortization flows" are automatically generated "derived business transaction (business transaction category 9000)" ? If yes, then it cannot be reversed unless the PMP is changed proberbly. To do that, the related postings need to be reversed first, then you need to execute TPM19 for the position to recalculate the derived business transaction again (make sure the flag 'Recalculate Immeduiately' is set".
Best regards,
Jasmine