Hi,
First: PlayMaker license is per seat.
The PlayMaker registration happens within the Unity asset store or on the hutongGame store, so once you bought your license, you can import the package in any of your projects, regardless of wether your computer is online or not.
The restriction is that the license belongs to you ( that what "per seat" means), if you install it on another computer for someone else to use it, then you should either purchase additionnal license ( there is a button on the asset store "Buy additional license"), or have that person purchase it. But it's totally fine if it's you on both computers. I have several computers and I purchased PlayMaker only once, because I am the one using all these computers.
Bye,
Jean