Hi,
Yes you can run your VM on an external disk such as a USB2 or USB3 disk.
It should not matter if you use another USB port, as long as the disk is mounted under the same folder name, the VM will work without complaining.
IF the VM does complain then it will say something along the line of "this VM has been moved or copied" .. answer "MOVED" and you can continue to use it as is.
PS: beware that disconnecting the external disk while you are running the VM can corrupt the VM beyond repairs, so make regular backups.
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Wil