Why a Type 82 concept can be a destroyer or cruiser

Why would a Type 82-like design follow the County class whether the successor was called a destroyer or a cruiser?

Because the type number describes the ship's purpose, not whether the navy labels the hull a cruiser or destroyer.

Royal Navy type numbers describe what a ship is intended to do. They do not fix whether it must be called a destroyer or a cruiser. A Type 82-like successor can therefore retain its intended purpose while being imagined at cruiser scale.