I'll make this quick and concise. You can change your companions without taking a long rest by opening up the Map and on the right side you can find the list of Waypoints you've found along the way. Along the list of Waypoints, select the Camp and you'll be teleported into your Camp and from there, you can change your companions with ease.
I don't know if anyone else has posted about this but I might as well spread the word because my friend and I discovered this during a character moment he had with Asterion. For spoiler-free, it did not go well and we were both stuck playing as the companions.
Have fun switching your companions either for story or party composition reasons.
Last edited by Sandblisz; 10/10/20 05:23 AM.