I've got a Cobra(Cimarron) large frame in 38spl. It also came with a spare barrel in 32? something or other caliber I've not ever seen ammo for, so I never used it. They are made of an alloy much like Heritage Arms(Rough Rider 6-shooters).
It's nothing to swap barrels within the same size of framework. So easy even Biden could swap barrels.
You either have a small or large frame and Cimarron derringer website will help you to determine what frame you have and spare barrels that will work. The barrels and replacement parts are quite cheap to pickup some spares.
I recommend you to stay with the small frame calibers in rimfire, unless you jump up to better made derringers in steel, like a Bond Arms that can handle more powerful ammos over longer periods of time. You can even get a Bond Arm derringer in 45 long colt where you can also shoot 410 shot shells if you want and barrels up to I believe 10".
Also, the trigger design is different on a derringer(at least the cheaper ones) due to many not having a trigger finger enclosure loop(open trigger design). It requires one to do a pull down and back motion with the trigger finger to overcome the firing sequence easier. If one pulls the trigger straight back, the pull feels like 15-20# before hammer break. One cannot overcome the way the trigger is designed either, to make it better(at least Davis/Cobra/Cimarron).