Editing a completed invoice to append item location details

I have sales invoices coming into AccountRight from a third party (Servicem8).  Sales Invoices are completed once they arrive in MYOB AR.  Sales invoices have a number of items on them, including inventory items.   I have 2 locations.  The Location of the items can not be passed through the existing API, so it comes through as blank, and MYOB AR will select the default location.    My question is:  Is it possible to edit the item location on an approved/ completed sale invoice?  If yes - will it correct the quantity of items at each location?

Thanks