how easy is it to change a catalytic converter on a peugeot 306

Dead easy.
Take it to Kwick Fit, go to the pub for an hour and it is done.
Could not be simpler.

changing the kat will damage the rest of the exhaust if more than six months old so better just replace the full exhaust the kat will unbolt and the rest will cut and are placed on hangers so it is quite easy fit all the pieces on the floor loosely compare to old system then start at one end work to the other hen you are happy with it bolt it up tight dont forget that a used kat is worth £20-40 scrap value as it will contain 2 grams of platnium

they are quite easy really two 10ml headed bolts join front pipe with springs and washers and exhuast clamp at other end probably 13ml heads this will not damage any of exhuast if done correctly make sure that no exhaust putty or gum is used before the cat as this will damage it