The answer is maybe. If the owner did works that affected the common property without approval, and then an insurance claim arose in relation to issues related to that common property, and the insurer knew that the owner had done those works, then the insurer might deny the claim. Note that an insurance contract is one of utmost good faith, so both parties have to disclose everything they know that may be relevant to the contract.
Similarly – if an owner did something with their property which didn’t comply with the law or regulations, such as using part of their property in a way that was in breach of the law, then an insurer could deny a claim. What I mean by that is for example if there were an area that did not meet the requirements for a habitable space, and an owner used it as a habitable space.
Hope that makes sense.