Which exhaust?

[MiiTCH]

I had a new exhaust system fitted last year, standard system with a Sportex backbox... When the new cat and centre pipe where fitted, it kept coming lose, so the garage welded the cat and the down pipe... And now I want a new sportex centre pipe for my car to make it a little louder, but I'm not sure if I will need a new cat as mine has been welded, or if I cut it, the new pipe will still fit?