1) If a wall is about to fall, it is permitted to rebuild it even if it as building of happiness. Even if it is not dangerous, (e.g. it is in an enclosed space) if there will be a financial loss, one may rebuild it during the nine days. (Shulchan Aruch 551)
2) A Jew who has a court-case with a non-Jew, should postpone it until after the nine days, as at that time the omens for Jews are not good. (Shulchan Aruch 551). Some say that one should postpone it until the first of Elul (Mishne Berurah ibid) Others say that one only need postpone it until after the tenth of Av, especially as the fifteenth is a happy day. (Ben Ish Chai Devarim 1)
