As shown in the image of the disassembled one, there's not any adjustability to that front element. It simply goes in place, or it doesn't.
The below reads to me like mostly CYA/revenue generation from Schneider, really. All they could basically do that a DIY couldn't would be to collimate it (if it even needed that), since there's no shims involved as shown in the image of the opened one.
FWIW
-Ed
"Here's what Schneider-Kreuznach says about messing with the SS-XL, among other alignment-sensitive designs:
Our ranges Super-Angulon (incl. XL types), Super-Symmar XL, Super-Symmar HM, Apo-Componon and Digitar can be only repaired at Schneider-Kreuznach. To optimize the optical parameter in the best possible way an exact re-adjustment of these lenses after repair is absolutely necessary."
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