May a person who accepts upon himself a personal fast eat a seudat mitzvah? For example, if a person finds himself at a bris on the day he accepted to fast, is he able to eat?
I am answering the OP, who is not referencing Yom Kippur. Yes, because a seudat mitzvah trumps a fast. There are a number of things that can override a personal decision to fast, such as, health, or even a simchat brit.