Is it permissible to change the intention of the Aqiqah from female to male after designating the sacrifice for a female?

Firstly: The 'Aqiqah (sacrificial animal for a newborn) is not designated by specific assignment like the Udhiyah (sacrificial animal for Eid al-Adha). Therefore, it is permissible to sell it after designating it or slaughtering it. The 'Aqiqah was legislated for the joyous occasion of a birth. For this reason, if you designated the ewe as an 'Aqiqah for your son, there is no harm. Some jurists, however, hold the view that it is designated by specific assignment, similar to the Udhiyah, and this is the madhhab (school of thought) of the Shafi'is.

Secondly: It is recommended to sacrifice two sheep for a boy and one sheep for a girl. If one sheep is slaughtered for a boy, it suffices. If you have already slaughtered one sheep for your son intending to slaughter another if it becomes easy, there is no harm. If you suffice with one sheep, the 'Aqiqah has taken place, and what you slaughter now does not take the ruling of an 'Aqiqah.