I am able to register mine even before preInit, and it works flawlessly.
The Oredictname of Dusts is "dustYourname". I know there are a few people who thought: HEY LETS MAKE IT "itemDustYourname"!, but those are just Hipsters.
I can't easily register ours before preinit because of the way Metallurgy is constructed. I could, but it would take a quite a bit of restructuring.
Well dang, time to rename all my dusts for IC2 again