Interesting... We add misc charges to existing receipts quite often. How else would you get the receipt amount to equal the invoice when there are extra charges on the invoice that you weren't aware of at the time of the receipt?

I know that we cannot prorate misc charges, but we use misc charges assigned to expense accounts all the time. After opening the existing receipt we simply click on "New Line". It defaults to "Misc Charge" in the Detail type (cannot be changed to anything else). When you click on the magnifying glass beside "Misc Charge" you can select any misc charge from the list that you have set up.

If we know about the misc charge at the time of the receipt, we add it at the time of the receipt since it's our only opportunity to prorate it to the inventory received on the receipt. We prefer this since it gives us a more accurate cost on each item so we can determine what our selling price should be. If however, we find out about a misc charge after the initial receipt, we add a new line for shipping, duty, brokerage, etc. and the cost goes to the assigned expense account.