Is it possible to have a multi-barrel set-up for a Ruger #1? That is, ideally I would like to change from a 25/06 to a 33/06 by screwing in another barrel. Are there any gunsmiths who can do this, and is is possible?

Possible yes, Practical no. I think you'll find the Thompson Encore to be better suited for that.

As Malm said, not practical unless you want to do it to change calibers and not use it as a switch barrel rig. It is a simple matter to rebarrel it to that caliber, the extractor is the same.