A question I wondered about was for a manufacturer team, do drivers just stick with a single chassis model through the season or do they bring a spare kart with a different flex/tubing size to the track; then register for the race whichever chassis performs the better of the two on that particular track.

Are there privateers that currently do that?

It used to be fairly common for Factory teams in Europe to bring several different chassis configurations to a track for testing and then decide based on that. I think homologation regulations might be more tightly controlled now so it doesn't happen that much anymore?

I'm not sure if that's allowed anymore. I think if you get your chassis working correctly, you can be fast at any track with that chassis. I don't feel that you need different chassis for different tracks.

-edit- Oh I see what you're saying. I thought you were asking if drivers could switch chassis between races on the same day.