If a person accepts Jesus as messiah, but doesn’t believe he was ‘god’, can they be Jewish?

In a word: no.

If they start to accept Jesus as ‘messiah’, that means they are embracing Christian ideology. That is their right – of course it is. But they can’t then claim to be practising ‘judaism’. To accept Jesus – or anyone – as maschiach WHILE our prophecies are not fulfilled, would be in violation of Jewish beliefs, yes.

Because of course the ideology surrounding Jesus is also that his death ‘atoned’ for the sins of mankind. This violates Torah. Torah states that no person can ever die for the sins of another human being. We are each responsible for our own sins.