There is a beta version available but without totally operational localisation... you have an PM...
But Lower Navarra is a very tiny area. The namely lower Navarra part of it is supposed to be attached to "normal" Navarra. Soule is only a barony that joined Béarn.
Not really enough place there to be accurate enough apart of rearranging a bit borders.
Personally, I only renamed Dax to Lapurdi, kept it into de jure Gascony, but added it to conditions to form Navarra.
Thanks for the PM
I think your edit makes sense considering the changes to de jure that seems to be include in the next patch(will probably wait to do anything about lower navarre, until the patch is out, and I can see how it effect things)