The Halacha, according to Hacham Ovadia (Yehave Da’at 3:12), is to recite the Beracha of Mezonot, not Ha’mosi, when eating Massa during the year, since it is not the normal bread. On Pesah, one recites Ha’mosi on the Massa because it is the only form of bread permitted. Hacham Ovadia (Hazon Ovadia p. 64) rules that if one wishes to eat Massa on Mosa’eh Pesah, the Beracha would still be Ha’mosi. Even though Pesah is over, and it is permitted to eat regular bread, the Massa does not lose its status, since bread is not readily available. This could be a common issue this year, in which Pesach ends on Mosa’eh Shabbat. If one wishes to eat Melave Malka, he may not have easy access to bread, especially in a hotel.
Some have the custom, dating back to the Vilna Gaon, to specifically make an effort to eat Hames on Mosa’eh Pesah. This is not because they could not wait until morning. Rather, it is to demonstrate that Hames is now permitted. Rav Salmon Musafi, would make a special new bread on Mosa’eh Pesah.
Rabbi Avraham Chamweh in the Machzor Bet HaBechira, the Machzor of Halab, records a custom for the father to takes a tree branch on Mosa’eh Pesach and rap the head of all the family members, blessing them with a “green” year of blessing, growth and prosperity. This custom is also brought in Derech Eretz and in Pesach Besion.
One recites Ha’mosi when eating Massa on Mosa’eh Pesah