The change of an award booking would be handled by UA MP, so it would be best if you contact them beforehand, especially since you will "have a short time at an U.S. airport".
Once the booking is correct, the ticketing desk at the airport will then be able to ticket it.
= Thanks everyone and especially KVS for all the help. I got it re-issued ... but almost missed my flight! The agent at CMH refused to believe that she could issue the ticket. She kept on saying, "Sorry Sir. There are no United segments. We cannot issue this non-United ticket." I was like ... "Um, it is UAL stock as its UAL miles". She would not have it. After arguing back and forth for 10 mins, she finally agreed to get her supervisor ... she kept on saying that the supervisor was "very busy". LOL.
Anyway, all's well that end's well.
Thanks.
Cheers,
A.