The expectation of the specification is obviously that the spine overrides are used for individual content documents, but we don't explicitly say that using the properties with a refines attribute is disallowed. Epubcheck will report such use as an error, however.

Suggest that we modify each definition where they say "The rendition:X property MUST NOT be declared more than once." to also say:

The property also MUST NOT modify Publication Resources using the refines attribute. Refer to #.#.# X Overrides for setting the property for individual EPUB Content Documents.