1st things first is make sure your stove is registered with BK, there's a certificate that comes with the stove and also the serial # on the back of the actual unit.
If the stove is not registered call them and register it.
Call your dealer, notify them that you need to replace your cat under warranty. They should take all your info and if they don't have the stove serial # on file, they should take that to.
BK may call you to confirm the cat needs to be replaced, they may ask you questions about it over the phone. They should mail your dealer the part, make sure you ask your dealer to include the gasket also. (now is the time to check and order any gaskets to)
I waited until my dealer had the actual part before I pulled my cat, (just in case) It should be take the old cat out, go to dealer, pick up new cat, drop off old cat.
FYI, all the conditions you describe as shorter burn times, more blue smoke coming out of the chimney under an active cat and lower heat output is exactly what I was seeing also, plus I had a ton more fly ash build up on the flame screen.