have only one skin in your folder then tell Q2 to now download any new skins/models.
Delete unwanted skins from your Quake2 tree. This includes the baseq2/players tree and also the modfolder/players tree for that particular mod. Custom skins will show up as game default skins if they don't exist on your system. If you have custom skin, name it the same name as the default skins you want to override. Then configure your Q2 client to NOT download player models/skins