Hi Gene, let me show my ignorance first: I don't think spinning the pins is compatible with peining them. But I could be so far out of whack on this I'm visiting Venus... Wouldn't be the first time. Maybe someone who knows something will straighten me out.
Most people do countersink the holes before peining the pins, so you should do at least some shaping prior to inserting the pins. For myself, I usually don't, just whale away and fill the holes with pin.
A couple caveats. If you hit hard it tends to cause the pin to bulge
inside the hole; peining lightly causes the tops of the pins to expand before the part inside. Both have their merits, but you have to be careful not to push the bolsters away from the knife by peining too hard and making the pins swell inside. Hope this isn't too convoluted a description, it's early...
Good luck, be sure to show us when you're done!
Dave