German culture as a whole shouldn't be renamed to Franconian, Franconian is a possible subculture.
I've had a look at your German culture setup. If you're aiming at a similar level of detail (to your French and Iberian culture split) and somewhat accuracy, a possible division for German could be (reusing also the Swiss culture):
Alemannic:
Alsace, Baden, Württemberg, Bern, Schwyz
Bavarian:
Bavaria, Ansbach, Ostmarch, Tirol, Steiermark, Salzburg, Austria, Odenburg
Franconian:
Lorraine, Luxembourg, Köln, Pfalz, Mainz, Würzburg, Hessen
(Upper) Saxon:
Sachsen, Silesia, Anhalt
Westphalian (actually Western Low Saxon, but Westphalian is more rememberable although not accurate):
Kleve, Münster, Hannover (Oldenburg if it's not made Frisian), Bremen, Magdeburg, Holstein
Wendish (actually Eastern Low Saxon, Wendish was the term for the Hanseatic towns east of the Elbe)
Mecklenburg, Brandenburg, Küstrin, Vorpommern, Hinterpommern, Danzig
Frisian culture could be introduced in Friesland and Oldenburg
All this is only my humble suggestion, and probably wouldn't work out in standard EU2, but looks really cute and might be nice for your scenario.