My local PBS station tends to broadcast (on 12.2) SD versions of shows like This Old House before the HDTV version airs (on 12.1) later that day or later in the week.
I know all about setting the advanced Tags CONTAINS HDTV option to only record the HD version, and that works. But I think it would be really nice if an episode of any show you have a Pass for could be replaced at any time if a higher definition version gets broadcast at a later time. I can see this as being an advanced option to "Re-record and replace show if HD version is aired later."