GETTING MY POLYMER 80 GLOCK 43 COMPLETE KIT TO WORK

I am confused. I bought a 22lr revolver a few months back, I desired to lengthen the barrel by about 2 inches so I requested where by I could buy a substitute barrel about the manufactures Web-site, they stated that the gun was registered to me from the atf with a certain barrel length and if I adjust that I would wish a whole new serial range.Coul