An airport change from MSP to SEA is highly unlikely to happen since the distance is 1399mi, which is far outside their limit of treating airports as being part of the same served region. I believe the limit is 200mi.

The other two, you can try, but since the trip is in May and not subject to the EU261 14-day rule, they are likely going to look for award space. Try checking if there is award space on one of those days that is still 70k FB miles. If so, there should be no issue. Just keep in mind that changes to FB tickets are not possible. The way it is done is that they will cancel your current ticket, refund the miles and taxes, then you buy a brand new ticket at whatever price it is now.