Floating licenses are managed by the Flexserver installation, which seems to base itself on the server hostname and MAC address (one of them, if there are several network adapters). As long as both the hostname and the MAC address remains unchanged, it will probably not be necessary to replace the license file.

However, if you do need to replace the license file, it's only a matter of sending the hostname and MAC address of the new server (found in hostid.txt in the Flexserver directory) to your Safe partner, and they should be able to generate a new license file fairly quickly.