One big question, If the purchase order has been sent to the vendor already will they honor the price you have listed?

You would think, but in the building materials world this isn't the case.  When pricing goes up on the supply side, all open POs are impacted.

You could import with VI but you would need the line key and the line sequence numbers on the source file and in the import job to update the line and prevent adding new lines.

You could import with VI but you would need the line key and the line sequence numbers on the source file and in the import job to update the line and prevent adding new lines.

A button script might work, to scroll through lines and update the unit costs... but how easy that would be depends on if there is a detail object method to re-trigger the Sage costing hierarchy logic. 

(Trying to reproduce the Sage pricing / costing logic in a script is not easy).

We actually did this a couple of months ago to address this issue but found that VI job didn't catch all the info so many POs are split between old/new costing.  We have identified what SKUs are mismatched, but its over 1000 line items between 60+ POs.