At least two recent anime series have had openings (OPs) or endings (EDs) that were unique to a single episode. The OP to Erased episode 11 was modified for dramatic purpose to carry over the suspense beginning in episode 10. Every ED for ReLIFE had its own custom music, combined with a mixture of repeated and custom visuals. I am sure there have been other series to do this sort of thing.
As a fan, I appreciate the extra effort the studios take in producing special OPs and EDs. And it is likely the artistic staff at the anime studios enjoy offering their fans these special glimpses into their series. From a production standpoint, though, I wonder how much extra cost a special OP or ED adds. Do they expect that enhanced fan appreciation due to these things will result in higher returns? Or are they, like the artistic folks, doing it "for the fun of it"?