The installment amount on the pledge does not change since all they did was adjust the payment.
 
We adjusted the payment application applied to the pledge to $0  and took the $100 and made it an application of donation.  Since the adjusted the application applied to the pledge to $0 it will still show as $0 on the pledge record.  If they do not want this then they either need to delete the $0 application on the payment or adjust/write-off the pledge if they will not receive the $100.