Gemara

Mishnah: If a house full of produce was breached, one may take produce through the opening;

R. Meir says, l'Chatchilah one may make an opening.

Gemara - Question: Why is this permitted? This is destroying an Ohel!

Answer (Rav Nechumi bar Ada): The 'house' is a mere arrangement of bricks without cement.

Question: Rav Nachman taught that one may move leftover bricks from building, because one could lie on them, but not if he arranged them (like a wall), for he set them aside!

Answer (R. Zeira): R. Meir permits only on Yom Tov, but not on Shabbos. (Rav Nachman forbids only on Shabbos.)

Support (Beraisa - R. Meir): L'Chatchilah one may make an opening and take the food. This is on Yom Tov; but not on Shabbos.

Rishonim

The Rif and Rosh (4:5) bring our Mishnah.

Ran (DH Bayis citing Rashi): We established the Mishnah to discuss an arrangement of bricks without cement. R. Meir permits breaching for the sake of Simchas Yom Tov because it is mere movement of Muktzah.

Rebuttal (Ramban, brought in Ran): If so, the first Tana, who forbids breaching, should consider the food to be Muktzah! A rickety Sukah is Asur due to a mid'Rabanan Isur. Even Stirah of a strong Sukah is mid'Oraisa only if he intends to rebuild it. Coins on a pillow or bed forbid it for all of Shabbos due to Bosis, even though coins are Muktzah only mid'Rabanan. Rather, since the Isur is not due to the food itself, it is permitted. An object is Muktzah Machmas Isur only if the Isur pertains to the object itself, or if it is a Bosis for Isur.

Rosh (4:6): We may take through the opening only if the 'house' was an arrangement of bricks without cement. Breaching it is forbidden only mid'Rabanan, therefore the food is not Muktzah. We say similarly about Tevel; if one transgressed (mid'Rabanan) and tithed it, it is not Muktzah. Since real Stirah is necessary to get food in a proper (sealed) house, the food is Muktzah. Even R. Shimon permits wood of a Sukah that fell only if the Sukah was rickety.

Rambam (Hilchos Yom Tov 2:9): If a house full of produce was breached, one may take produce through the opening.

Question: The food should be Muktzah, since the house was sealed at the start of Yom Tov!

Answer #1 (Magid Mishnah): The Rashba permits only if the house was rickety; the owner anticipated that it would be breached.

Answer #2 (Magid Mishnah): The Ramban says that an object is Muktzah Machmas Isur only if the Isur pertains to the object itself, or if it is a Bosis for Isur. This is correct; the Rif and Rambam agree.

Answer #3 (Milchamos Hash-m 19b): The Mishnah (and Rif and Rambam) discusses a house that was breached before Yom Tov. Chachamim permit to take through the hole; R. Meir permits to make a new hole.

Poskim

Shulchan Aruch (OC 518:9): If a house full of Muchan produce was breached, one may take produce through the opening.

Riva (brought in Beis Yosef DH veha'Mordechai): R. Meir permits breaching for the sake of Ochel Nefesh because it is mere movement of Muktzah. This is like our custom to use Muktzah ashes, which resulted from a fire on Yom Tov, for Ochel Nefesh, e.g. to cover a meat pie.

Question (Beis Yosef): If so, we should permit Shechitah of a Chayah or bird on Yom Tov and to do Kisuy ha'Dam using Muktzah ashes (but this is forbidden)!

Answer (Taz 7): The meat is permitted even if Kisuy is not done. This shows that Kisuy is not a need of Ochel Nefesh.

Beis Yosef (OC 518 DH Aval): The Ran connotes that the Rif holds like Rashi. This is wrong. The Rif and Rambam do not say that we discuss arranged bricks. They explain that the Gemara established the Mishnah to discuss an arrangement of bricks without cement to explain how R. Meir permits breaching. It was not concerned for Muktzah.

Mishnah Berurah (44): The Shulchan Aruch specifies that the produce was Muchan. If it was a storehouse, it is Muktzah.

Bi'ur Halachah (DH Bayis): Since many Rishonim hold like Rashi and the Rosh, if the food was in a solid house one should be lenient only in greatly pressed circumstances.

Kaf ha'Chayim (65): We discuss a totally sealed house, or when the key was lost (and the house was locked).

Shulchan Aruch (515:9): If Reuven sent food to Shimon via a Nochri before Yom Tov, and the Nochri was delayed and brought it on Yom Tov from outside the Techum, even Shimon may eat it.

Source (Beis Yosef DH Kosav): The Kolbo and Rashba permit, because there is no concern lest Shimon tell the Nochri to bring more.

Rema: This is only if he expected to get it from before Yom Tov. If not, it is Muktzah to all Yisraelim, for any food of a Yisrael must be prepared from before Yom Tov.

Rebuttal #1 (Magen Avraham 27): The Rashba did not stipulate that Shimon must have intent from before Yom Tov. The food is no worse than Hefker food that one finds, which is not Muktzah.

Rebuttal #2 (Taz 518:7): It is permitted to everyone except for Shimon. Even Rashi and the Rosh permit food that was in a sealed house when only an Isur mid'Rabanan prevented one from getting the food.

Mishnah Berurah (72): One may rely on the lenient opinion in pressed circumstances. Those who permit Muktzah on Yom Tov permit in any case.