For the MiG-29 Fulcrum, the pilot can only be customized as part of the cockpit(-view), so it is not customizable for external views. Other aircraft have the pilot/helmet/... as part of the aircraft livery so it can be customized. I made this (https://forum.dcs.world/topic/380055-support-for-full-liverypilotcockpit-mod-in-user-folder-without-breaking-pure-textures/ topic before I knew it was a MiG-29 Fulcrum specific problem.