It doesn't really matter whether the phenomenon is due to listener acclimation, component change, or some combination of the two. The point of "break-in" advice is to get people to reserve judgment until their perception of a new component's performance stabilizes. With some loudspeakers and listeners, that takes a while. For others, it happens fast.
Like callas01 with his new Dynaudio Contours, I experienced some favorable and unfavorable swings and moments of regret and disappointment when "breaking in" my Dynaudio Confidence C2 speakers. I really don't care how much of that was actual break-in (probably not much) versus acclimating to a different sound (probably most of it). It doesn't matter except in internet pissing contests. What matters is that I came around to love them after a few months, I've owned them longer than any other pair of speakers, and I don't want to replace them.
Unlike my experience with the Dynaudio C2s, the break-in/acclimation period has been fast with some other speakers I've owned. But ironically, those are the speakers I got rid of the soonest.
HT: Dynaudio C2, Contour S CX, 2x BM14S, Aperion surrounds, Simaudio Titan, Marantz AV8801, Oppo 103, Linn Majik DS, and a Pioneer Kuro
Stereo: Dynaudio Focus 160, Simaudio W-5 LE or Luxman M-600A, Linn Akurate DSM, 2x Rythmik F12G
Other interests: motorcycling, skiing, being active