If a person accepted a personal fast, is he allowed to make a siyum on that day even though he is fasting and won't eat? Also, is there something special about a personal fast day (other than not eating) that precludes someone from making a siyum?
There is a custom to fast on a yahrzeit unless it is on a yom tov. There is also a custom to make a siyum. I have seen once a rov making a siyum just before the end of the day and eating afterwards a seudo for the siyum attended by many people.