Hi daltorias! Thanks for your question! In MS Store, PFX3, there is no cabinet mode. You can't use 1 Steam Account in 2 different computer. However if you play online in one computer and offline in the other, you can use the same Steam Account.
If you want to play offline, please follow these steps:
1. Disconnect the desired device from the internet
2. Start Steam in offline mode
3. Highlight Pinball FX3 from the Steam library and press the right mouse button
4. Select Properties
5. On the "General" tab of the popup window select "SET LAUNCH OPTIONS..." button
6. Type -offline in the text input field then press OK
7. Start the game from Steam
Also, if any other user has another idea, please share with us!
Hope it helps!