I run a a cluster and someone msg'ed me asking if they can donate a game server with 150 days on it. Can he transfer that server to my account or would i have to sign into his account to access it?
Sorry, but at the moment is is not possible to transfer the ownership of a server.
BUT: the other user can grant you full access (guest access rights) to his server so you can configure everything and add it to your cluster. (will not work with PS4 or XBOX)
Just keep in mind, the other user has to pay for the server. If the runtime is over, you will lose all the data without access so make sure to download everything you need before it ends. (again, will not work for PS4 or XBOX)