Make sure you have the electrical permit and inspection (even you tell them it will be done with the help of your experienced friend, they will give a pass as long as the works meet the code) If the basement is only PARTIALLY finished, the property tax will remain unaffected.
What did you build in your basement? Not all type of basement reno need permit. Also depend on whether it's single or row house. Ask your contracor for advice, see if they can make it up for you.