You cite the Tos Yom Tov on 63a stating that even according to Rashi there couldn't be an actual lav of baal yaraeh and bal yitmatze before the Moed actually began. However, how then do you answer the Rashi in Baba Kama 29B that clearly states the opposite?
Eli, los angeles, CA
The Tosfos Yom Tov himself actually hints at an answer to this question by saying "and like the Magid (Mishnah) in Perek Gimmel from Hilchos Chametz." The Magid Mishnah there (3:8) understands that even the Rambam holds that there is no Bal Yeira'eh until Yom Tov. He explains that when the Rambam seemingly says that a person who still has Chametz after six hours transgresses Bal Yeira'eh, he means that he will transgress Bal Yeira'eh at the start of Yom Tov. This is probably how the Tosfos Yom Tov understood Rashi in Bava Kama (DH "mi'Shesh").
All the best,
Yaakov Montrose