Mech Invoice Rework!

As a Mech sometimes it can be very annoying when working with a customer who changes their mind last second after being so hell bent that they want something. for instance there was a customer that i was working with the other day who said everything was good then just as i created the invoice they wanted something different which then led me having to make a completely new invoice. I think there should be an option where mechanics can REOPEN and add/ take away things on that invoice instead of having to make a new invoice, then just have the price automatically update depending as to what gets done.