I don't know that "biologically impossible" is the right descriptor --I would go with "psychologically odd." It is quite possible, even common, to initially hear an unfamiliar piece of music as "noise" or "boring" or "repetitious" or "dissonant" or "disturbing," and later hear it as having quite different qualities once you know it better, or have a context for it, or have become familiar with the genre. However, this is generally because you have become better at perceiving it as intended, not because its traits have changed.
In this case, you seem to be expecting to be able to learn to associate an arbitrary set of characteristics to a given piece of music. It is possible that some specific dissonant, postmodernist piece could be merry and uplifting (perhaps the Rite of Spring, if we count that as post-modern?), but it seems fairly certain that that was not the general goal of the creators of the genre. The pleasures of every genre are not the same, if they were, why would we need so many? I suspect that you are pursuing a theory that associations to music are arbitrary, and that post-modernist music seems like a good candidate, since its specific artistic choices are sometimes deliberately randomized, or dogmatically formal. But the pleasures of this genre, for those who appreciate it, are conceptual. Merriment is not really a concept, per se.
Surf pop is an inherently merry and uplifting genre. But Brian Wilson, one of its chief architects, turned it, in his later work, towards themes of melancholy, isolation, nostalgia and despair. It's possible some post-modernist genius could perform the same magic in reverse, and create merry dissonances. (Compare Desafinado, which, while not merry or uplifting, is an entirely lovely piece built deliberately around "wrong" notes and dissonant harmonies.) But it is unreasonable to expect a randomly selected example of the genre to be that song.