As far as I can see, editing the VM through the UI will "undo" the changes to the XML file.
Wouldn't USB assignment on a port level be a better choice than the current one? I just assume that this is an issue most people will face eventually. If you for example add two Logitech unifying receivers or Xbox360 adapters they will obviously have the same name. I assume most people would rather use specific ports for VMs instead of having to worry about this issue?
Edit: Some sort of setting on the VM page that toggles the format vendor/product or address would be awesome.