Is it possible to negotiate the position rank in an UK academic job offer?
Yes, you can always ask about salary and position for any job you are applying to. They won't stop considering you because you asked for more money.

While we are researchers, and love what we do [citation needed], in our society we need money and work for money*, thus bringing money to the negotiations is (or should be) an obvious part of the "finding a job" process.

They can say "yes", "let's negotiate" or "no". Just be prepared for all, and make the decision as you see fit.

*you wouldn't work for free, would you?