Yes, you can remove only certain spirits. You just need to have a mental connection to the spirit you want to remove. I can be anything that uniquely identifies that particular spirit. After you have that, you can begin the actual banishment of that spirit - that will leave any other spirits alone. But if I were you, I would do a complete cleansing of the house. You are actually help any ghost you are able to to move on into the light because they are really trapped between two realms.