What happens if an officer enters my home without permission?

It is impossible to answer this question without knowing the officer's state of mind, why the officer entered your home, and what the officer did upon entering. But NO, you absolutely cannot use or threaten to use your firearm on a police officer just because you think he has entered your home without permission.

You are allowed to protect your home, including from the authorities, from anyone who enters without permission. If an officer insists on entering I would suggest a lawyer is a more appropriate weapon than a gun.

Law enforcement officers cannot enter your home without permission unless they have and arrest warrant, search warrant, or other court authorization, or an emergency situation exists, such as someone being attacked, fire, etc. In any situation, I would advise extreme caution in using a firearm (I assume you are referring to a Concealed Pistol Permit when you say you have a "CPL"), in any situation. Situations in which one can use a firearm can be an extremely complex legal issue. Additionally, if law enforcement enters your home, legally or not, it is possible, in fact likely, that more officers are in the area and you would be outnumbered and outgunned.

This depends on whether he has a right to do so. A warrant. Hot pursuit of a criminal. Etc.