Bobbermad

Got a yamaha 535 which I want to make a bobber buy I've seen some done in hard tail is that conversions by welding or a different frame ? Confused and was thinking maybe buying different frame and swapping the virago parts over but do you need to get it checked or retested or is jus an simple mot ? Well hope someone could help even with tips pics of yours please helps as want this but I'm lost as you can tell .