My take is the warranty will not be voided completely if you have a problem, just the area that you modified.
That is only my opinion, I would not attach anything to the bumper for a bike rack. Ask him to attach it to the frame.
I have seen a Jayco that the owner replaced the rear square bumper with a piece of square steel, which was attached to the frame with extra gussets and his bike receiver was attached to it.
2011 351RLTS Eagle, Mor/Ryde suspension & pin box
06 F350 Lariat PSD, SRW, LB, CC, EGR delete kit, 16K DrawTite hitch, Timbrens, TST TPMS
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