if cut and crowned professionally you stand to gain accuracy, not lose it, with the shorter stiffer barrel. done improperly, you stand to lose accuracy. if you cut it to 18.5" and the smith f*cks your crown or the bore near the muzzle, you are SOOL and stuck with it unless you rebarrel - so consider the 19" length. this will also leave you with a bit of leeway in case you damage the muzzle later down the road and need it recrowned.
youll lose ~25 FPS of velocity per inch of barrel cut.
**edit
honestly, thinking about it some more there really wont be that much of a difference from 22" to 19", and you are putting out about $100 and risking a decrease in accuracy if its done improperly. consider living with it the way it is and possibly putting the money towards a shorter barreled factory carbine, or a short barreled bolt-action like the Ruger Compact.