I'd wait to see whether they allow fans in for the game - as NCAA, NHL< NBA games are not allowing unnecessary persons into venues - as for your train ticket - AMTRAK announced :

No change fees on bookings made through April 30, 2020. We are waiving change fees so you can book travel on Amtrak® with confidence, knowing you have the flexibility to change your plans.
Shouldn't have a problem - if you have a problem, email corporate , they've always been great when I had a problem.