These boards are very large and there is no visible underlay. If the boards were regimental, they would have a cornflower blue base and a rose secondary underlay, visible. He had this appointment or right to wear the uniform of the 7th Dragoons pre-war; there are photos of him wearing it at the 1913 'Kaiser' maneuvers.
I posit that he's wearing the same detachable shoulder boards, Bavarian general's cords on red base not visible, with the gilt '7' added between the lower crossed silver Bavarian FM baton arms, as he wore on the uberrock worn in the photos of him at the 1913 maneuvers, and also below. The size, and lack of visible base and underlay colors also support this. This was also the practice, I believe, of non-Prussian officers receiving appointments to Prussian regiments.
Can anyone corroborate or correct?