Also for Glocks there is the Advantage Arms conversion kit to shoot 22LR. Mine have performed well and its a quick upper change, with its own mags. They cost a bit, but you are practicing with the same trigger, etc as your EDC, which makes it worth it to me.
AA also makes kits for 1911s as do others, but I have no first hand experience with those.
Nice to know that people are shooting 40 from their Glock 20's... This has always made me nervous. A friend of mine always tells me it's fine to do it in his and invites me to (he never has) and I never wanted to be the guy that messed something up. I also want a 20 but didn't want one until I start reloaded for ammo price reasons... I may have to get one soon!
I am shooting 9mm from my 40 cal. Glock 35 and 40 cal Glock 22 with Lone Wolf barrels. The 35 barrel is ok, but the 22 barrel shoots 8in. above point of aim at 25 yards. Basic attitude at Lone Wolf customer service is they don’t need you and they expect the same. Barrel has been returned and they will hopefully get back to me in a few weeks.
I have a Glock 35 that I shoot 40 S&W, 357 Sig, and 9mm with. It takes maybe 30 seconds to change barrels. The 40 and 357 Sig use the same magazines but you need to use a different one for the 9mm. I also find the after market barrels of Lone Wolf or KKM shoot better.
I have read that you can shoot 9X23 from a 1911 in 38 super without modification and also from a full size witness steel in the same caliber, with the usual caveat about extractor performance. There is quite a difference in SAAMI specs (max pressure 36500 vs 55000 for 9X23) so I'm not sure I'd ever go there.
Pertaining to barrel changes the FNP/FNX 40s from Herstal can be fitted with a factory 357sig barrel. They even marketed FNPs that came with both from the factory. Have thought about buying another FNP40 to convert to 357sig 'cause people want too much for the factory FNP357s