All the state variables in the OpenZeppelin ERC721 contracts have private visibility. That means, if one is trying to override functions like: ownerOf(), isApprovedForAll(), it is simply not a matter of overriding the functionality. You have to redefine and manage state variables like _owners and _operatorApprovals etc.
Isn't it better to just re-write the entire contract by yourself? Please provide some clarity if you think I am missing something.
Thanks in advance for your help.