There are a lot of dual warfare qualified bubbas in aviation, having done something first before getting there. As Thisguy said, you can wear both. I have my dive pin and my silver dolphins, I just rotate them when I am unforunate enough to be wearing my khakis, which is all the time right now! It actually states it in the uniform regs, if you are that interested in looking it up, you must wear your primary warfare qual you are working in up top, this really doesn't apply to us, who would put the wings of gold anywhere else?
As for switching the dive pin to gold (BDO), that's a new one for me, must apply to 2nd and 1st class divers or something. I have seen a shiny gold SCUBA pin on marines, but marines like anything that is shiny and foo foo for their uniforms (who loves ya) so that probably is definitely not what you were referring to.