If a stipulation was made before Yom Tov:[1] If one stipulated on Erev Yom Tov before the start of Sukkos, before Bein Hashmashos, by [verbally[2]] saying that he reserves the right to use the decorations throughout all the period of Bein Hashmashos of all the eight days of Sukkos, then the decorations are not forbidden in benefit and are permitted to be used and eaten throughout the holiday whenever one chooses.[3] [This applies whether they are hanging on the walls of the Sukkah or the Sechach of the Sukkah.[4]] However, the stipulation is only valid if one stipulated to be allowed to use it during freely during Bein Hashmashos. If, however, one stipulated to simply reserve the right to use or eat the decorations once they fall off the Sukkah, then this stipulation is Halachically worthless.[5] Likewise, if he only said that he is stipulating to reserve the right to make use of the decorations for the entire Bein Hashmashos of the first day, and did not stipulate regarding the Bein Hashmashos of the other days, then they become prohibited in benefit from the second day and onwards.[6] If he only said that he is stipulating to reserve the right to make use of the decorations for the entire Bein Hashmashos of the second day and onwards, but did not stipulate regarding the Bein Hashmashos of the first day, then they become prohibited in benefit on the first day and even on the second day and onwards.[7] If, however, one stipulated and said that he reserves the right to use them throughout the entire Bein Hashmashos without explicitly mentioning neither the first day nor the other days, then we assume that his intent was on the Bein Hashamshos of all the days of the Holiday, and it is thus permitted to be used and benefited from whenever he chooses, whether on the first day or any other day.[8] Likewise, if he said that he reserves the right to use the decorations whenever he wishes and did not mention at all the word Bein Hashmashos, then he may use and benefit from it whenever he chooses.[9]
The custom:[10] Practically, today the custom of the world is to hang all forms of decorative sheets and other ornaments and to remove the ornaments from the Sukkah [on Shabbos and Yom Tov] whenever they desire, such as due to rain or thieves, even if they did not stipulate on them from Erev Yom Tov, being that the custom has become to allow doing so and it is hence considered as if one stipulated.[11] Nevertheless, initially it is proper to stipulate on this matter from before Yom Tov.[12]
Who should stipulate?[13] [In addition to one who plans on removing the decorations during the festival needing to initially stipulate beforehand, as stated above, furthermore[ even one who does not plan on removing the decorations from the Sukkah throughout the entire festival should nevertheless stipulate on Erev Yom Tov if he knows that the children may come to eat from the edible decorations during the festival [or make another use of it].
[1] Admur 638:7; Michaber and Rama 638:2; Beitza 30b; Rosh 24:9
[2] Thinking alone does not suffice, and the stipulation must be verbalized. [Hagahos Maharsham 638; Piskeiy Teshuvos 638:4]
[3] The reason: The reason for this is because at the time of Bein Hashmashos, which is the start of the day, when the holiness of the Sukkah was meant to befall it, the holiness did not befall it at all, being that he stipulated that his power and right be retained over them and hence it ends up that the decorations were never designated at all for the Mitzvah. Now, although they are hanging in the Sukkah there is no belittling of the Mitzvah involved in using them being that they have not been designated at all for the Mitzvah. [Admur ibid]
[4] Setimas Admur ibid who does not differentiate
Other opinions: Some Poskim rule that today we are no longer expert in the stipulation, and thus no longer stipulate regarding the decorations that hang by the Sechach of the Sukkah, however by the Sechach that hangs by the walls we do stipulate as some Poskim rule that even the walls themselves are permitted in benefit. [Rama 638:2; See Taz 638:7 and M”A 638:8]
[5] Admur 638:8; Michaber 638:2; Hagahos Maimanis 6:16; Semak 93
The reason: The reason for this is because they were not stipulated to be used at the time that they were hanging on the Sukkah, and if so it ends up that during Bein Hashmashos when they were hanging on the Sukkah the holiness of the Sukkah befalls it. Now, once the holiness befalls it, it no longer leaves as a result of the original stipulation being that the stipulation only helps to prevent the Kedusha from befalling the decoration [and not to revoke it or end it], and thus once the Kedusha befalls it, it no longer leaves. Accordingly, even if the decorations fell from the Sukkah they may not be used. [Admur ibid; Beis Yosef 638; Levush 638:2]
[6] Admur 638:9; Rama 638:2; Orchos Chaim in name of Ramban
The reason: As each and every day of Sukkos is considered its own independent Kedusha, and the Kedusha of that day befalls the decoration in the beginning of the emntrance of each day that was not stipulated upon. [Admur ibid; Taz 638:5]
[7] Admur 638:9; Taz 638:5; Orchos Chaim in name of Ramban
The reason: As since the Kedusha befell the decorations by Bein Hashmashos of the first day it no longer leaves it throughout all the days of the festival, being that they are considered like one long day regarding this matter to be stringent and not to be lenient. [Admur ibid; Taz ibid]
[8] Admur ibid; M”A 638:7; Rashal Beitza 4:3
[9] Admur 638:10; Michaber 638:2; Bahag
The reason: As since he stipulated to retain the right to use them whenever he desires, the period of Bein Hashmashos was likewise included within this stipulation, and it hence ends up that the holiness never be
[10] Admur 638:11; Rama 638:2; Darkei Moshe 638:5
[11] The reason: Some have given the following justification behind the custom: Since the custom of the world is to remove them from the Sukkah [on Shabbos and Yom Tov] due to worry of it being stolen or due to rain, it is therefore considered that whenever a person hangs valuable items in the Sukkah as a decoration, certainly his intent is only for the sake of the custom, which is to remove it from there in a time of need. This then makes it considered as if he has explicitly stipulated upon them a stipulation which allows him to remove them from there when he needs. Meaning, that he does not separate from them throughout the entire Bein Hashmashos of all seven days of the festival, and it is therefore permitted from him to remove it from there whenever he wishes, even when it is not raining, and even if there is no worry of robbers at all, as the holiness of the Sukkah never befell them. [Admur ibid; Taz 638:8; M”B 638:24]
[12] Admur ibid; Rama ibid
[13] Admur 638:18; M”A 638:4