The P-40 fix-ups are out now in Patch 2 so you are free to go ahead with your P-40 skins.  Make sure that you use Patch 2 and the latest hi-res pack to export your template.  Please note that the skin and sound folders to the P-40B has been renamed to p40c.
P-40B and P-40C and their export versions are acceptable skins for the P-40B.  P-40D and E skins are acceptable for the P-40E.  No skins for variants later than the E are acceptable at this time.