These cards stay in your inventory until used, so its posible to keep the card from the second charge in your inventory after purchasing a new blessing (of any type). You cannot summon a new card without first using/destroying any previously summoned however.
\aITEM 38770502 1980886312:King of the Court\/a
\aITEM 994774282 214929446:Queen of the Court\/a
\aITEM 1466373733 -318369286:Prince of the Court\/a