That is true. It's also the way he's asking for me to do that for free. First of all, they are trying to act as if we talked about that for a while now and it's a thing that I HAVE to do even though is not in the contract.

I sometimes give them freebies if it does not require that much work and if the client is very nice and asks in a very polite way. "You know, I know we haven't talked about this and if it is not too much work and trouble on your behaf, I would deeply appreciate if you could do also add that in".
If there's something along those lines and indeed, there's not too much work involved I would give it to them for free. I also take in consideration his previous attitude towards me and our contract and also if there is any chance I would work with him/her in the future.