Posting to let you all know about PokeStock's subprogram that allows you to edit the C-Gear skin of your save file.
C-Gear skins are saved into the save file, with encryption as you already know. PokeCGear exports these (probably encrypted) skins in a format ".psk". Poke Skin or whatever. C-Gear skins are 256x192 pixels and can also be exported to bmp format.
Over at Project Pokemon you can find this PokeStock and the translated version, in addition to the C-Gear Skin Exchange Thread where you can download past skins or upload new ones.
C-Gear Skin Exchange Thread
PokeStock Main Download Thread
Kaarosu's Translations of the Subprograms Thread
Hope this information helps in whatever you are trying to do