Valid.
Though the only things you can’t do are things that change the value of the fare, really. (And the date) I’ve gotten a name misspelling corrected, and I ordered the distilled water for then-husband’s cpap, no problems. And of course you book all port adventures and dining on your own.
The only time I’ve ever felt stifled was when I looked at fares late at night when my TA was asleep and had to wait for her to snag that concierge room that was available for only $300 total over what we were paying. Nerve-wracking. And easily controlled in the future by NOT looking when the TA is closed.
I would be far too aware that she might have 50 other bookings on that cruise and my priority wouldn’t be first. I would rather do it. But once you’ve booked with the TA you can’t change that stuff on your own.