If CMS is requesting a specific service be submitted to it in a specific format and you have that request in writing, you should provide it to that payer in that format.
While I do not enjoy altering stated coding guidelines myself, it is sometimes necessary from a compliance standpoint. For instance, it doesn't have to be "written" somewhere that you attach a "GA" Modifier to a service for which you have a signed ABN (we're talking a Medicare Bene here), it is simply sound and compliant coding.
I believe it is the responsibility of the practice/physician once the agreement is made to participate in the Medicare program. The Federal Register searches I've done are not showing me exactly what I need to see.
Hopefully someone else will have the specific document or mention of it.
Of course, when we say that CMS guidelines supercede stated guidelines elsewhere, it would only apply to either Medicare or Medicaid patients--dependent upon the specific situation.
Good luck.