To answer crudely: yes, because no medicine without civ, and/or no, because herbs and stuff (I remember finding a zine about herbal transitioning, which I find more interesting in theory than in practice), or, much like my answer to the insulin question, because one could always kill an animal and consume its hormones without the use of medicine or anything I would consider part of civilization.
But I take issue with issue this herbal approach, and the gland-harvesting one, and similar fantasies, because of the fact that the discourse of transsexuality (the way we talk about it) comes from the mental health establishment, which defines it as a mental disorder with a path of therapy and medical treatment. So here, as with other supposed disorders, to accept the diagnosis and treatment of these professionals, even if it makes you feel better, runs totally counter not only to anti-civ anarchy but to anarchy generally. And to imagine people retaining such a discourse while leaving the rest of civilization behind strikes me as an absurdity only possible through a liberal framework. This does not mean post-civ people could not take such herbs, or drink hormonal-gland smoothies, but that their motivations would differ; they would act out of more playful, wilder, less serious, less belief-based, less civilized urges.
But a deeper question emerges: What relation could we trace between gender and civilization? One could make a strong argument that these are linked at an incredibly deep level, that to live against the one means to live against the other, that resisting one must mean resisting the other. If we accept this, then the question becomes very different. The definition of transsexuality, but also the definitions of transgender, genderqueer, or any not-necessarily-medical conception of gender deviance intertwine so deeply with civilization/gender that calling civilization into question means calling all these identity-forms into question, for having no real ground, for playing the same game, only in different (deviant) ways.
The question then becomes, as you suggest, one of self and society. If uncivilizing means (among other things) refusing the ways society genders us, it means a refusal at a level close to where we locate ourselves in society (our identities). If no transgender experience will exist, neither will any experience of gender as such, and I would consider gender transition a useful metaphor for this transition to the post-civ, not in the way it implies arriving at a destination, but in the sense of being fed up with the place society puts us every day and setting off from there, to who knows where, maybe to nowhere.
P.S. Hot-button topics like this remind me of daytime talk shows.
( edited as part of the eprime project, see http://anarchy101.org/9200/what-think-about-eprime-language-possible-relevance-anarchy