nop33
I couldn’t find any restrictions for foreign persons in the respective T&Cs or FAQ neither. So it should be possible, since the linked SwissPass account supports every country.
(As opposed e.g. to the current 1-month trial GA offer, which is limited to just the neighbouring countries of CH for foreigners)
Just make sure that you understand what you can buy with that prepaid credit and what you can’t. Rule of thumb: It works for any PERSONAL ticket or day pass which you can buy online with the SBB Mobile app.
Shelling out e.g. 1000.- on half fare tickets within a month in order to gain that 20% additional discount means quite a busy month! 😉