I asked the man at the BD Winter Champs, Solihull this question, except for a Jaguar jumping saddle and he said they could adjust them to a certain extent. He didn't expand on the point much more than that though really.
Ive got one and the saddler said the trees can be tweaked for minor adjustments. My friends got two and one was altered from M to MW by the saddler and the other from M to XXW but this one was sent back to Jaguar for a different tree.