I've always seen classpects as a whole as intentionally flawed ways of categorizing people. People change, often drastically, but this is not something being in a story always allows. You are expected to have character retain most of their original personality and motivations even through arcs when this is commonly not the case in real life(especially when your starting point is a thirteen year old). I think that classpects are just another way that SBURB seems to force people into an expected story structure and force them to grow in ways which are not natural to real life. Applying this to gender, I think that SBURB would likely base the gender of your class on your presentation at the time of playing. This is the most upsetting answer, but I think it fits the themes I take away from Homestuck the best. Sometimes, you have to break out of the bounds of SBURB, out of the bounds of being in a story, and out of the bounds of society to be happy.

This also gives some credence to many trans readings of characters where said character seems to rebel against their chosen classpect or accept it solemnly with some sense of duty when it really seems like they don't feel it fits them.