Hi Vet,
Think of the example of Driant... born in 1855, and into the chamber of deputies in 1910...
In 1914 he went back into uniform and served as a Chasseur officer.... he drove Joffre mad because he voiced his opinions directly to his friends in the chamber and to Gallieni....
Like Driant he must have taken a commission for the duration of the war, but that did not exclude him from his position in the chamber...
I am not sure where to find it anymore but there was a good French article about the problems Joffre had/and his dislike of... members of the chamber in uniform.
Best
Chris