Hey Ipearson,
I spoke to the guys behind the spares counter about his thoughts on warranty and mods as I was probing about Nissans reaction to a 3" exhaust on my ZD30. He said if anything went wrong with the engine, that could even remotely be connected to the change in exhaust pipe, it would void warranty.
He also made mention of a guy who blew an engine and Nissan found he was using Ryco filters. Nissan Warranty department said the warranty was void but the contact at Nissan arced up in defense of the customer as they didn't want to be the one to tell the customer he wasn't covered. Customer must have been a big unit :-D Apparently they came around in the end. This is what I was told so don't know the truth of it, but it sounds possible and even likely.
I see car company warranties just like insurance companies, they'll always look for a loop hole to get out of it, especially if it is a major claim.
Just my 2 bob's worth, keep the change ;-) I'm sure others can help further and perhaps from personal experience.
Deejay