I haven't had the MCT ISO default to Home in ages, even on my laptop with an 8.0 Core OEM embedded key. YMMV as others report that their key is being detected and used.
I skip entering a key and I get the full menu of all the Editions available to be installed.
And like Bree says, if you were already running an activated 10 Pro, change key with the generic Pro key will work. No need for the ei.cfg IMHO. Use one if you want, but its not a mandatory type thing.

EDIT: And if this the first install or Pro on that device, and its running Home, enter you Retail Pro key via change key. It will verify it, upgrade, and activate.