Of course `before-hack-local-variables-hook' runs before any local
variables are set, so there is no "correct" order that a user can use
in .dir-locals.el to define a new style: `c-file-style' always applies
before any other variables.
​Thanks very much; to check I understand, you're saying that at present it's not possible to do this all in .dir-locals.el; I'd have presumably to define the style in my Emacs init sequence (or anyway, load it before visiting the directory)?