Each vendor can differ in process from moving a license to a new machine, or how many machines a license can be installed/ active concurrently.
Boris FX: Serial Number Activation or UPID activation Transferring Boris FX Products to another system
Chaos Group: License Server version 5.0 provides licensing of the Chaos Group products without the need for any physical devices to be plugged in your machine. It allows you to easily activate more licenses right after the purchase and provides a way to stay offline while using your products when you need to. It is still compatible with existing USB dongles, in case you need to use your licenses in this way. Chaos Group Licensing
RE:Vision Effects: Transfer Floating License Server to New Machine
Maxon: One Machine per license, You can install on as many machines as you would like and release to new machines as needed. More Info.
Video Copilot: Machine upgrade or need to transfer plug-in to a new machine: The process is to delete the plug-in from the old machine and re-install and re-license on the new machine the same way as you did on the old machine. More Info.