Hi Bud,
Yes they will pass MOT emissions tests.
"Would any exhaust centre know" - the answer is yes unless they are complete muppets. Would I personally take to kwik fit - probably not as I always recommend taking any parts I sell to an experienced specialist.
I can't imagine you would have a problem as it's just undoing bolts, swap out, do up bolts... As long as they have the tools to remove a possible stubborn bolt you will be fine
Chris