The License that I have is locked to the wrong dongle, if I have multiple dongles on the system.
The Licensing Software for MXE shares the software with other applications released from other vendors. There is nothing special about the MXE dongle. It is a piece of hardware just like the ones from the other companies. If there are multiple dongles in the system when the software is being installed, the software is set up to use the first dongle that it sees in the system. This is what it will use for the URL for the license request page. If the dongle that is plugged in is not the one that you want to have a license for, then you should unplug all other dongles from the system prior to installation of MXE.
If you forget to unplug the other dongles from the system, this still does not pose a major problem. It means only that you have the license locked to a dongle that you purchased from another company. This is perfectly fine as long as the dongle is a FLEX-based dongle. It does not have to be a MXE dongle.
There is no reason to rehost the license. The other dongle will work with the MXE dongle if needed. If there is a need to rehost the license to a different dongle, then you will have to incur the cost in rehosting the license.