This would involve creating new textures for both the static and rotating prop, and altering the appropriate meshes so as to use the new .mat/.tga file pair.
A potential difficulty arises when selecting different plane skins, if only certain skins are to use the new prop texture. The only way I see to enable the use of a second texture alongside the original texture is by setting some dscriminating element in the plane's class, such as a range of dates compared against the date set in the mission file. If the mission date is within the range, the metal prop appears; otherwise the usual prop texture is used. But then this restricts its use to a more limited interval.
Of course, a new slot could be created for a 'special' variant of the plane. If the rest of the plane is similarly bare metal, the skin textures could use layers and/or .mat file parameters to accentuate the specularity (shininess).
Perhaps a more accomplished plane modder could chime in with some trick I'm unaware of that would permit to use an additional texture that involves no difficult hoops to jump through.