Siman 653

It is a known matter that the etrog and all the species are set aside for their mitzvah for all the days of the festival, unless one made a condition regarding them that he does not withdraw from them during every twilight, as I wrote in siman 649. We also wrote there that one should not do so, see there. According to this, the etrog is forbidden for eating until after the festival. However, to smell it is permitted. But the hadas is forbidden to be smelled, for a reason that will be explained.

And so our sages, of blessed memory, said (37b): A hadas of mitzvah—it is forbidden to smell it. An etrog of mitzvah—it is permitted to smell it. What is the reason? A hadas, which stands for fragrance, when one designates it—he designates it away from its fragrance. An etrog, which stands for eating, when one designates it—he designates it away from eating—and not from smelling it. That is to say: the ordinary sense of the matter is that when they set it aside for a mitzvah—they designate it away from that for which it stands. Therefore, the etrog was designated away from its eating, as it stands for that. And the hadas was designated away from its fragrance, as it stands for that. But if he explicitly designated the etrog even away from its fragrance—it is certainly forbidden.

The Tur wrote that one who smells the etrog—our teacher Simcha wrote that he should not recite the blessing "Who gives a good fragrance to fruits," for its primary purpose is not for fragrance. But the Raviah wrote that one should recite the blessing. Thus far his words. Therefore, our teacher, the Beit Yosef, wrote: Since they disagreed whether one recites a blessing over it or not, one should refrain from smelling it. Thus far his words. And the opinion of our teacher Simcha is not understood: Is not the blessing "Who gave a good fragrance to fruits" for fruits intended for eating? And why should he not recite a blessing over its fragrance? And perhaps specifically regarding an etrog of the mitzvah he says this, and it requires further study. And also on Shabbat it is forbidden to smell the hadas, for it was set aside for all seven days. (And I saw the Magen Avraham who wrote as I have written, that specifically regarding that of the mitzvah one should not recite the blessing, see there.)

It is a known matter that designation is not a substantial act. Therefore, as long as one has not lifted the species for the mitzvah, they possess no sanctity and are not muktzeh for the mitzvah. Nevertheless, if one designated them from the eve of the Yom Tov to be for the mitzvah, muktzeh automatically takes effect upon them, since he set them aside of his own volition, and their law is like all other forms of muktzeh. Nevertheless, they are not forbidden for benefit until he lifts them for the mitzvah. However, on Yom Tov there is no practical difference regarding this muktzeh, for they are permitted in handling, as he did not set them aside from handling; on the contrary, he set them aside to recite a blessing over them and to handle them. But on Shabbat they are forbidden due to the reason of its being muktzeh (so it appears in my humble opinion).