Siman 653
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א הֲדַס שֶׁל מִצְוָה אָסוּר לְהָרִיחַ בּוֹ, אֲבָל אֶתְרוֹג שֶׁל מִצְוָה מֻתָּר לְהָרִיחַ בּוֹ מִן הַדִּין, אֶלָּא שֶׁלְּפִי שֶׁנֶּחְלְקוּ אִם מְבָרְכִים עָלָיו אִם לָאו יֵשׁ לִמְנֹעַ מִלְּהָרִיחַ בּוֹ.
1 It is forbidden to smell the myrtle. Containing 2 paragraphs It is forbidden to smell the myrtle that is used for the mitzvah. Technically, it is permitted to smell the etrog, but because there is a disagreement about whether or not to bless on it, one should refrain from smelling it.
ב עָבֵד לְהוֹשַׁעְנָא וְלֹא אַגְבְּהֵה לְמֵיפַק בָּהּ, שַׁרְיָא בַּהֲנָאָה.
2 If [one of the four species] was made for [use as one of the four species] but was not lifted to fulfill an obligation, it is still permissible to get benefit from it.