When can you transplant asters? I'm in Minneapolis/St. Paul.
You're 2 zones colder then me mjaorhyn so I'm not sure how helpful my advice would be.
I move my established asters in the spring mainly because they are blooming now and when they finish it's late in the season. But, I bought a few asters now and did plant them so if I had to I would transplant now with a really big root ball to disturb then as little as possible, water well and mulch and hope for the best.
I think in general fall bloomers are better moved in the spring.