i've thought about this a lot, even so it's not possible. honestly, i think the biggest reason i'd say "no" is because of all the self-righteous "i told you so"s i'd get from people who were convinced it was just a phase. i wouldn't want to give them the satisfaction. gotta cling to what few shreds of dignity i have, even if it's to my detriment...
i don't want to be transgender. i don't want to live the rest of my life knowing that i'll never be a normal man, or be able to function like one 100%. i don't want to be unable to have my own children. i don't want to have to "come out" to every future partner even long after i pass in every other aspect. i don't want to have to deal with others' disgust, hatred, patronizing, and confusion for the rest of my life. but that's the path onto which i was thrown, whether i like it or not.
if i could change something so that i never had to deal with any of this in the first place and have not been born transgender at all, that would be a much more tempting offer--though even then, if i hadn't gone through what i have, i don't know what kind of person i would be now. maybe a much worse one, considering the environment in which i was raised. maybe a much more judgmental, ignorant person like the family that still refuses to accept or acknowledge me today. maybe i'd have grown out of that on my own, but i still wouldn't have the experience. and experience is something i value, even when it's negative, because it always has something to teach and it shapes who we are.
i find it really hard to imagine being comfortable in this body. i tried for so many years, but the harder i tried, the less comfortable i actually was. so being able to change that, to remove that discomfort, definitely has its appeal. i could go on and live a normal life. i wouldn't have to explain my body to anyone or warn them about it as if i had some disease. i wouldn't have to worry about which bathroom i'm supposed to be in or whether or not people knew what gender i was. i wouldn't even have to think about it.
...but it would also mean that everything i had gone through up to this point was for nothing, and i don't think i could live with that. all the stress, fear, depression, and arguments; one person after another trying to beat into my head that i was wrong and didn't know what i was talking about, and how hard i had to work to keep my chin up and get through those conversations, not backing down about being sure of who and what i was regardless of what they wanted me to be. i think it really would kill me to just flip a switch and say "ok, you were right; i'm actually a girl after all."
that said, i do wish such a thing existed for those who wanted it. imagine noticing those feelings, being able to get a treatment that worked, and saving oneself from years of risk and hardship. in a world where this kind of thing is finally recognized as a condition that should be respected and treated like any other, and not just some childish attempt to be different, a pill like that would be a dream come true for a lot of people.