To my knowledge, one has always been able to change the channel name - so that part is not new.
I thought the check is real-time, so there shouldn't be a delay. Can you clearly describe your situation, i am not sure i get it? E.g.
(1) had pvt channel named A
(2) renamed A to "A test" - that worked
(3) trying to create public channel "A" fails now, showing such-and-such error
What answers in the forum say that "Roku support had to change the name"?