Besides the Seudah of Purim is there a minhag to eat another meal in the morning before chatzos yom?
There is a custom to eat another meal in the morning, before chatzos. This is probably in deference to the opinions who write that one should eat the seudah early. However, many are not particular about practicing the minhag.
Sources: See Nit’ei Gavriel, chap. 70, no. 1, and siman 23 (at the end of the book). Although Shelah (Megillah) writes that the seudah should be eaten early in the day, the common custom is to eat after Minchah, which is the ruling of Rema; Yaavatz; Derech Hachaim; Kitzur Shulchan Aruch. Several sefarim write that this is the common custom: Teshuvah Me’ahavah (290); His’orerus Teshuvah (492); Eretz Tzvi (121), and others.