Only IF the part is the cause of another failure. There is some law, can't remember the name, that states this. Ex: If your battery dies and you have lowering springs, they can't deny warrantying your battery because you're lowered. BUT if your shock/strut blows and you have lowering springs, they won't warranty the strut/shock. Unless you swap back to stock before going back to the dealer.
My understanding is that in Canada, there's no overall law that is similar, but each province has its own consumer protection acts. You may want to read up on what's included in the one for BC.
I've had all sorts of warranty claims denied, mods or not. If the dealer doesn't feel like sucking up the repairs, they'll try and put it on the customer. Even if the car is stock, they can just blame it on lack of maintenance or abusive driving. Just do what you're going to do as far as mods go and don't worry about it.
