The present installation is not compliant with the National Electric Code (NEC) and never was. Cable TV companies are notorious violators of this rule. I know that you do not want to hear what I'm saying here. You want someone to say it's fine here's how you do it. Anyone who does so is being grossly negligent. If you do what you want to do, and it causes a fire or electrical damage, your home owners insurance carrier can walk away from the loss, That is because you caused the loss and it is a breach of your policy to do anything that might cause a loss. Insurance contracts are in a unique category of contracts called "Contracts of Utmost Good Faith." Such a contract obligates all parties to that contract to do the best that they can possibly do to avoid any breach of the provisions of the contract. That includes not doing anything which violates the legally adopted construction codes of your locality. No matter who here tells you how to violate the NEC it will not absolve you of your obligations under the law to avoid causing a property loss. If you do this anyway then on your head be it.existing mast with cable tv and old burnt out lamp