Thanks. So, they are not specific to the darkroom/interactive editing (in other words: the reason I didn’t see a difference in my export experiments is not that they don’t affect export; rather, they don’t affect anything, at least not with my locally built and optimised setup).
I interpret @priort’s response to imply that those settings would actually affect generic builds (triggered by BINARY_PACKAGE_BUILD (march=generic, mtune=generic). Is that the case?