Are the Sukkah decorations Muktzah on Shabbos/Yom Tov? Ideally, if a stipulation was not made, then the decorations are Muktzah on Shabbos/Yom Tov even if they are food items, being that they are forbidden in being eaten [or used].[1] It would thus be forbidden to move them even for the sake of saving them from getting stolen, or from rain damage. However, in light of the above custom to move the items even without stipulation, the decorations are not Muktzah even if a stipulation was not made.[2]
Removing the decorations on Shabbos/Yom Tov:[3] If one desires to leave himself the option of being allowed to remove the decorations of the Sukkah on Yom Tov [and Shabbos] due to the rain or worry of thieves, then [aside for initially making an explicit verbal stipulation, as stated above ] he is to beware not to tie the decorations to the Sukkah in a complete knot, in which case it would be prohibited to undo on [Shabbos or] Yom Tov, and rather he is to attach them with a loop. [Thus, they may only be untied if it is not a double knot or any other knot that is forbidden to be made on Shabbos.[4] If they are tied with plastic zip lock strips, then seemingly they may not be cut free on Shabbos and Yom Tov.[5] In addition to the above, they may only be removed on Yom Tov or Shabbos if doing so does not involve the destroying prohibition. Thus, if they are stapled, or nailed in the boards, then they may not be removed.]
[1] Admur 636:6; Rama 636:2; Tur 636; Bahag; Mordechai
The reason: As since the decorations are forbidden in use therefore, they have no purpose throughout all the days of the festival and are Muktzah. [Admur ibid]
[2] Admur 638:11 and 17 which refers even on Yom Tov
[3] Admur 638:17; M”A 638:9; Darkei Moshe 638:5; Aguddah 1:9; M”B 638:24
[4] See Piskeiy Teshuvos 638:7 and our corresponding Sefer “A Semicha Aid for the Laws of Shabbos” Volume 2, Sections of Boneh Vesoser and Tying and Untying
[5] The reason: As even if cutting them would not be viewed as forbidden due to Soser due to them being similar to other non-sturdy vessels, nonetheless, since it is not being done for a Shabbos need, therefore it should be forbidden. [See Admur 314:1 and Ketzos Hashulchan 119 footnote 18]