You've been able to change your Engy spec for quite some time now, but it requires reading some book and levelling Engy back up from the very beginning.
Oh. And if you originally had Goblin, de-specced ( so to say ) and levelled it up 'till you got Gnome, you then won't be able to use anything crafted from a Goblin engineer.
And that includes things like the Jumper Cables XL, of which a Goblin can normally craft but both specs can use.
*insert witty, or morally correct comment here*