Open …\Steam\steamapps\common\SpeedRunners\Content\ (Steam: right-click the game › Manage › Browse local files)
Back up Characters\Cosmonaut\animation_variant05.xnb, animation_atlas_variant05.xnb, heads.xnb, win_variant05.xnb, win_atlas_variant05.xnb and UI\MultiplayerMenu\Lobby\characterPortraits${sheetN}.xnb
Copy the zip's folders into Content\, replacing the originals (the zip keeps the game's folder layout)
Start SpeedRunners, pick Cosmonaut Comrade and skin variant 05. Verify integrity of game files in Steam puts the originals back any time.