Looking at the info sheets on Briess's webpage, I see their extracts already contain some Carapils malt, though it doesn't really say how much. What, if any, effect would this have on formulating a recipe?
Are you talking about their DME/LME? In terms of recipe formulations you don't take it into consideration. Most of the brewing software I've played with just treats it as extract. The only consideration is the color...ie Amber, Dark, etc.