Is it permissible to eat from an animal slaughtered entirely for Allah, and is it permissible to divide it like an Udhiyah sacrifice?

As long as the questioner has not presented any words indicating a vow, then the slaughtered animal is a voluntary charity. Voluntary charity becomes binding only upon its actual transfer (قبض), and if it has not been transferred, there is no reprehensibility in eating from it. If a person sets aside something to give in charity and then decides not to, it is preferable for him to proceed with it, but it is not obligatory, because the recipient does not own it until it is transferred to him. Nevertheless, refraining from eating from it is more appropriate and better, so as not to fall under the general meaning of the Prophet’s (peace be upon him) saying: "He who takes back his charity is like a dog that returns to its vomit."