Question is all in the title.
The reason I’m asking this is because I want to use that guid as a key which can authorize requests (RPC’s) to for example move the player.
If the player’s guid were to suddenly change, he can’t really do anything anymore if I’m using a system like this.
Not sure about guid, but you can use NetworkViewID of networkView you use to handle your networking operations. As long as you keep your connection, it will be the same. In case of reconnection, it depends on who instantiated this object - if object was instantiated by disconnected client, NetworkViewID is likely to change. Note that GUID is not just number, it is a struct consisting of number and enumeration member saying if it’s allocated or scene NetworkView. You probably figured it out already, but maybe someone else will be looking for it in future.
On the side, I don’t think guid would change for any reason, but have never used it.