What Is Rider Switch and How Does It Work?
If Guests in your party can’t or don’t want to board an attraction, you don’t have to miss out!
If a child does not meet the height requirement or a Guest does not wish to board a particular attraction, no problem! With Rider Switch, one adult can wait with the non-rider (or riders) while the rest of the party enjoys the attraction. When the other adult returns, they can supervise the non-riding Guests, and the waiting adult can board the attraction without having to wait in the regular line again!
This is from Disney website! If a CM does not honor insist and get someone else. They made need more training.
There is no way I'd be spending my time insisting and waiting for a manager over Rider Swap on vacation.
Like ArielSRL said, sometimes they allow it for guests who don't wish to boards, and sometimes they don't, whatever the policy says.