The extensions might work if it's a Euro car but if it's a US car the extensions will not get rid of the CEL.
Ecutuninggroup sells catless DPs and software/tune that will remove the CEL. They cannot guarantee their software will remove the CEL on other brand downpipes though apparently because there is only one value they can modify/manipulate. So if you really wanna get rid of it maybe purchase their DPs and tune.
PP-Performance said they can get rid of the CEL with their tune but they are not in the US so kinda depends where you are located.
Btw... My CEL is on and I could care less. It sounds so badass that the little light doesn't bother me.
Brian