There's a product in the Harley world that you put on the inside of the tubes and is supposed to prevent the blueing but I don't first hand know how well it works. There are two, from the company that makes Kreem Gas Tank liner, called Dyno Kote and Blue Shield.
Another 'ol school trick is to coat the inside of the header pipe with grease or a film of oil before first starting. It will smoke a lot but not hurt anything and as the grease or oil burns off a carbon layer forms on the inside of the tube insulating enough to prevent the blueing.
I haven't tried either of these personally, they're just things I've heard about that might work.
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