Okay so I copied and pasted it. (I am so going to wear you out on this.  Sorry!)   Renamed it p51d_1.   Now I have copied my .bmp file into the folder, overwriting the default.   I can see it in the viewer.  Looks pretty good actually.  LOL.   I thought I would mess it up but so far so good.
Is this what I need for it to show up in offline mode?   Once I know how to get to that point I may actually try and do a skin for real....