THE 2-MINUTE RULE FOR P80 GLOCK 19 GEN 3 FRAME

I'm confused. I bought a 22lr revolver a few months in the past, I desired to lengthen the barrel by about 2 inches so I questioned in which I could buy a substitute barrel about the manufactures Internet site, they claimed the gun was registered to me through the atf with a specific barrel size and if I improve that I would need a brand new serial