No. I'm assuming one does not do it.
Bob, I agree with you completely regarding the complexity of proper scientific blind testing. Thing is though, you and others taut the notion of "warm up" as though there is some profound difference to be had. Almost as though one is not hearing another verse in the song they are listening to, simply because the device hasn't warmed. if the difference is anything appreciable, it should be easily recognizable under any kind of simple blind test, that one can perform with the help of a friend. Be honest, the differences we are speaking of (writing about) is so subtle that you should ask yourself if it really matters in the grand scheme of the enjoyment one should derive from listening to music. I listen primarily to Grateful Dead. They sound phenomenal regardless of the playback medium. Now I can tell that band from another band one hundred percent of the time in any kind of a blind test. Easy, right? Well, IMO so too should folks be able to tell the difference between cold/warm in any kind of blind test. It doesn't have to be scientific to demonstrate definitively there is or is not a difference. Just something to satisfy ones own belief, which at times can be delusional.
Look, if you or whomever else hears a difference one way or another, and this somehow effects your overall satisfaction of the listening experience, more power to you.
Also, note that as depicted in your post, you are ABX'ing a Gungnir MB and Bifrost MB. In this case it is two different DACs, which in my view would be easier to distinguish among versus the same DAC cold or warm (albeit still difficult). Nevertheless, I remain appreciative of the input you are providing. Obviously you do know what you're talking about, have the credentials, the gear and wherewithal to do all of this.
If there is any consolation to all of this, you (and Jude's latest post) does offer proof to the extent I'm very much inclined to believe you and your measurements of the Yggdrasil.