In the past (more than 2 years ago) i had my xONES issued by a carrier different from the first. Back then I was always using a (real) TA, since i could just email him for changes etc.
I was worth every penny he was charging, since I was usually changing my routing midstream once or twice and also nested other tickets with the RTW. He managed to add them to the same reservation and checking luggage thru on differen tickets was never a problem.

I am still reluctant with all the changes of countries which you can enter to use RTWs.