In an HQ environment, you should be able to update any transfer order with an Origin of Local and a status of Open or Partial and have the changes sent via HQ to the store where the same order has an Origin of HQ. The originator of an inter-store transfer order should be able to make changes anytime before the order has been committed.
For inter-store transfers in, perhaps a flag or something could be added to notify the originating store that the transfer order has shipped from (been committed at) the remote store. You'd have to block changes after that time.
Additionally, an inter-store transfer out should not be Closed until the remote store has acknowledged receipt of the merchandise.
Even more, serial numbers should not need to be entered at both ends of this process...
But for now, I'd be content with the initial suggestion.
Tom