Hi, my client is using one plan for entering manual sales (let's call this a placeholder plan), that plan has a price of $100 (as a placeholder price). Is there a way to change the invoice amount after they have created the invoice?

I guess the other way would be to change the price on the plan before they create a manual backend sale, would this be a feasible way to do it, would changing the price of the placeholder plan affect any other previous plans created from it?

See attached image.