If one forgets to recite Ya’aleh Veyavo in Birchat Hamazon, but remembers before Hashem’s name at Bonei Yerushalayim, he goes back. If one realized after that, but before starting the next Brachah, he recites the extra Brachah as printed in some Birkonim. If one already began even the first word of the next Brachah, one must begin Birchat Hamazon again.
The Harachamon for Chag is recited.