I have a Jamis Bosanova and use it for almost everything. I tour on it, I commute, ride in town, group ride, country ride, etc. I am currently running the stock Alex wheelset with formula hubs. This bike has bb5 disc brake BTW. I am using 32c Vittoria Randonneur Cross tires for touring and dirt road riding, which they are great for. They are a bit on the heavy side for city and faster riding. I am wanting to get a second wheelset and put a set of 28c slick tires for those rides. I am now wondering about the cassette, I have a tiagra rear derailleur and a 9 speed sram 12-26 currently. I would not mind putting a 12-32 MTB cassette on my fat tire wheelset for touring and rough road riding. That would mean I need a MTB rear derailleur. On the skinny tire wheelset I would like to keep the gearing higher with a 12-26 or something close.
Would a MTB rear derailleur work correctly when changing wheels with such drastically different cassettes? What about other solutions to make this wheelset viable?