Nope, it kicks you.
I've seen people say otherwise, but I was just in a room, I was the one to receive control when the host left, but it just kicked all of us, about 8 people. The host even knew it would happen, forewarning all of us because it was Spa, the room would self-destruct when he left, just like created courses.
Maybe it glitches sometimes and doesn't, IDK, but the same also happens when people are using homemade tracks, always a DC for everyone, so I have to assume the exceptions are just glitches.
In any case if you get lucky and get into a Spa room second on the list, and it does hand you the room, you can't change anything about the track, if any settings at all.