I bought it on nwa.com -- and the change was only an hour difference and connecting through DTW rather than IND, with no fee due to involuntary schedule change.

So, maybe the ticket does not need to be re-issued?
What if I show up at the airport and it's not re-issued?
If they re-issue, can't they back out the upgrade and then give it right back?

I think I'll wait and see...