Q.I want to transplant some hydrangeas
I want to transplant some hydrangeas from east side of house (right next to house) to backyard. Our “white” hydrangeas currently bloom great in August/September, but our purple hydrangeas rarely bloom at all (they are all planted within 15 feet of each other).
A couple questions –
1) Is mid-October an ok time to do this? I live in NE Iowa.
2) Will the additional afternoon sunlight affect the blooming of these plants?

Answer #1. Fall is the perfect time to transplant. The plants can be making a new root system during the winter, and won't have to do this next spring.
Answer #2. I doubt the additional sun will affect blooming on the hydrangea. Of course, they prefer afternoon shade, but since your summers are of less duration, all you might need to do is water a little more frequently than in their previous location.
The only thing that might affect blooming for the next couple of years is the actual transplanting. Don't worry, it won't be permanent.