I have a crate of out of date beer/bitter by 6 months, tastes watery, can I resurrect it in some way? I found a case of Scottish beer / bitter that I had forgotten about, it is out of date by 7 months, which normally would not stop me but it tastes watery. My question is can I re-ferment it or add something to resurrect it?
I seriously doubt it. What happens over time is that chemicals giving the taste decays, and you cannot magically make them appear. You could perhaps add something to give it taste, but then, is it still beer?

Refermenting (could be done by adding sugar) will give carbon dioxide and alcohol, but not more taste.