THE SINGLE BEST STRATEGY TO USE FOR P80 GLOCK 17 FRAME

I'm perplexed. I bought a 22lr revolver a pair months in the past, I desired to lengthen the barrel by about 2 inches so I questioned wherever I could buy a substitution barrel to the manufactures Web site, they stated the gun was registered to me from the atf with a specific barrel size and when I change which i would need a different serial range