The statement "I am a man" is either:
a potential issur Gavra (acceptance upon oneself), in which case there is no chaticha deissura which is an Issue cheftza (article that is designated to become forbidden), rather a Shavua see note.* Also See ran Nedarim 2a.
- An admission הודאת בעל דין כמאה עדים דמי,but since it contradicts reality and has no effect other than a false statement in the past. see Yevamos 88a-b where it says clearly: eidus that a husband is dead cannot stop her children from another marriage being Mamzer if the husband shows up.
If this is considered option 2 an admission, then it is a Shavuas Shav (false oath) because she is saying "I am a man" and she is a woman not a man.
This is because the only ever recorded Chazal that mentions a man turning into a woman is when Leah was pregnant a 7th time and Hashem turned the male fetus into a female i.e dina see Rashi Bereishis 30,21 but that was a miracle and done by G-d Himself, not by human surgery c"v.
If this is option 1 an acceptance for the future to do Mitzvos of a man, it is a Yad sheeino Mochiach.
Since putting on male clothing is forbidden the very fact that she is intending on being a mumar (reccuring transgresser) by completely disregarding one of G-ds Mitzva shows how not intent on keeping extra Mitzvos she is, so this is a Yad sheeino Mochiach see Making a neder without specifying verbally and there is no evidence that she is making a Shavua in the future to accept mens commandments. So no she does not have to keep Mitzvos intended for men.
*An an acceptance upon oneself in the future even without a reference to the word Shavua can be a yad (secondary type) of Shavua see Nedarim 8a האומר לחבירו נשכים ונשנה פרק זה עליו להשכים.