Warhammer 40k - can I use a space marine captain model as Marneus Calgar?

I would think most gamers have proxied (used another model, or toy, or counter, or empty soda can) to represent something else to try it out, or see how it works in their army.. sometimes whole armies are proxied. No gamer I know would have a problem with you doing it. It's a game of toy soldiers, it is supposed to be fun and you are supposed to pay it together and that is the view point Games Workshops games are written from. Tell him to stop being such a .