Thanks for using Fusion. I don't believe we have a command to switch USB device between VMs.
I am not sure how your application interact with USB device, so if you connect your USB device to Mac host, and enable shared folder for different VMs, then you can access USB device at the same time.
This does NOT work when your application have special requirement (USB device connected only).
If shared folder doesn't fit for you, you may try Mac UI automation tools to control the USB connection/disconnection. Such as Sikuli or ATOMAC.