Adjust payment schedule after partial payments have been made.

[HVACArmStrong]

I'm halfway through a $3000.00 project that I've taken a deposit of $800.00 for and have recieved several other payments for that weren't payed according to the original schedule.(late and short payments) no big deal except that now we've added (and subtracted) to the total amount to be invoiced and when I edit the invoice payment schedule I can't enter the payments that have been made already. I can't enter a date before today and when I update after editing it shows payments are due but they've been made already.