Stop to Auto Altering Client Price When Unit Price Is Changed

Could you please update the issue that arises where if we go back into an invoice to edit/add unit price, it changes that cost in the client price field? 

Sometimes, when making the invoice for the client, we do not yet know the unit price (our cost) so we put that equal to the client price until we receive the pricing/PO from our vendor, and then change it at a later time. This creates a huge potential at some point for either 1) sending the client an invoice that has a lesser cost than what we are charging them because altering the unit price changes the client price, or 2) altering the proper accounting that is recorded. If the client price field could just stay static, or if we could have an option where we decide if the unit price affects the client price, that would be greatly appreciated. 

In addition, as you know things get very busy, so when someone is going back to add in one cost (unit cost), they have to remember or highlight the number in the client price field, then copy it so they don't lose that number, then go into alter the unit price, then go back into client price and paste it back in that field so it is correct. This also takes additional time, and we are trying to of course be as streamlined as possible. This addition would REALLY help out for all reasons above. Thank you!