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.

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.

Just wondering if you came up with a good way of doing this.  We have several vendors that even though they have had our POs since the end of last year, they are still pushing through price increases on product that has not shipped yet.  Since these are sole source suppliers we basically have no choice but to take it.   Thanks in advance.

Or receive at the updated price and the difference flows through as a purchase variance

It will only be a variance during Receipt of Goods if the item was a Standard Valuation item.  Otherwise, it will be received at the cost on the PO AND the PO will be updated with received cost.  I just tested this with a Lot, Std, and FIFO item on a PO - all with an original cost of 15.  I received at 20 each.  There was a variance for the std item, nothing for the others, and the PO now shows a cost of 20 each. The only variance at that point would be if the invoice was at a different cost.  Note that the cost is put into inventory when you do ROG - it's too late to get it right with a ROI.

I have a client with the same issue. They do ROG without the invoice number and want the correct cost in inventory for commission sake.  It is good to know someone already tried VI. I started looking at scripting but it would just be nice if Sage added an update utility.