Yes, you can indeed but you will have to go to the main train station in  your city (not a local ticket agent) and you need to do so before the departure date as indicated on the ticket.  Nonetheless, you will still loose about 15%, I believe as a handling charge.

Probably depends on the date of the ticket. There usually is a timeframe as to when you can get  a refund for certain things. And a ticket will have a date and time on it. If it's a year old no luck in getting a refund. But if it has only been 24 hours or shall I say less than 24 hours you may have a chance! Nothing is guaranteed however!