Thought I'd share an experience with Rider Switch and a specific time a CM did tell me my 5 year old DD "did not qualify" for Rider Switch because "there was no Rider Switch at this attraction."
It was for Toy Story Midway Mania and because there's no height requirement to ride, the CM told me there was no Rider Switch available.
I calmly explained that she didn't like the spinning and jerking of the ride and that as I understood, Rider Switch could be used when someone didn't want to experience the attraction, regardless of the reason or the person's height.
The CM eventually allowed us to switch, but it was several minutes before he made up his mind. I just remained as pleasant as possible after pleading my case and stood watching him scan FP's without further comment until he made his ruling.
I think the point other posters were trying to communicate is that you MAY get push back from CM's on certain attractions. Both my kids are very tall which does cause an issue at times. When I see a CM looking my DD up and down as I request a Rider Switch, I make sure to inform them that it's an issue of not wanting to ride, as opposed to being too short to ride. Usually they nod and it's done. But not always.
Knowing this ahead of time can help you plead your case. The information from the super savvy Rider Switch folks here was the reason I knew how to approach the situation when I was told no. It can and does happen.