So maybe another way to think about this problem, (whose previous terms aren't quite of the same interest to me now), is that its not a problem of identity at all but one of the meaning of praxis.
Without having read much about praxis as a concept ( see Arendt, Friere, even the Greeks), it now seems to me that praxis is the dialectical third term between theory and action, but more specifically mind and matter.
I'm not sure the problem comes out of historical materialism and hence the avante-garde, but it seems that the key of praxis is that it focusses on the creation of social relations (and hence self) via the creation of material life, or rather, the creation of material life is done with social relations as its ends:
This is to say it is not a question of the creation of "mythology" but a creation of self. That is by changing one's material circumstances in the knowledge that those material circumstances will in turn change oneself. There is always a "leap of faith" because of this moment of non-agency, because one can't predict fully how in creating new material circumstances one will make changes to one's self. So this is the connection between any praxis and revolutionary act, that it operates within co-ordinates that are of the future. Or as you put it, "putting one's self in situations where something has to happen".The materialist doctrine that men are products of circumstances and upbringing, and that, therefore, changed men are products of changed circumstances and changed upbringing, forgets that it is men who change circumstances and that the educator must himself be educated. Hence this doctrine is bound to divide society into two parts, one of which is superior to society. The coincidence of the changing of circumstances and of human activity or self-change [Selbstveränderung] can be conceived and rationally understood only as revolutionary practice. —Karl Marx, "Theses on Feuerbach, III"
In this way a personal mythology might be a way of how a praxis self-relates, how it appears to itself, and can thus be a productive motor for change.
I then wonder how to contrast this with self mythology that is constructed for the gaze of the Other, a sort of ego-ideal, which would imply that currently existing material and social circumstances hold the more determinative role over the personal character. This might present ones mythology as a type of false consciousness. It is a dress up or make believe or a reflection of the desire of the Other. It is a type of end rather than a process, it doesn't commit to a process of becoming through constitutive leaps.
I remember previously I was wary of those who self-mythologise as a type of self-aggrandisement, a type of escapism, a type of dandyish showing off. I also felt that it can alienate people who care about that person and wish to share in them in some way, and also have contributed to them in some way. And so maybe here an ethical concern additional to the one above arises, and comes out as a concern of social practice. That is, that these leaps into new material-symbolic relations (however small) not just be a solipsistic exercise that escapes, but one in which these leaps are made through collective negotiation so that these new symbolic spaces can be shared as meaningful. This movement acknowledges the subject as collectively constituted, and doesn't seek to posit the creation of self outside of sociality. The latter of which in denying the relationality of the individual creates a disjunctive "fantasy world" of self that can only be enjoyed by themselves and denies the collective social space etc etc
So in the continual feedback loop of creation of self, one has to take two leaps (which can't be separated): the creation of new material circumstances and also the creation of new forms of social relations. This transformation must be done together so that a meaningful way of relating to one's (potentially new) material and social totality can be shared.
Finally I wonder if nowadays, the hope for transformation through material change has been deprioritised as being all but too hard.
