 No, it doesn't dilute the intention in the least. It merely adds to it. No, I really believe that. Sometimes we have such a passion in our heart for something that we pray for to the exclusion of other things. But if we don't, I think that it's absolutely appropriate to add as many intentions as we want to a rosary or when we go to Mass. You know, God is pretty big. He can carry it all, as the saints are too.