The date is the only thing that's different as far as I can tell.
In fact by just ignoring your new_opt.img file and copying the rest of the files to both the US and UK folders, your browse by folders works as a "UK" centric ie "proper" date
I'm still trying to get the fonts hack to work but it just ignores my fonts (ie combining things as per pepaks mods earlier) so I'm still digging around.