אורח חיים תרנ״גOrach Chayim 653

Se’if 1א׳

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.

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.

Se’if 2ב׳

עָבֵד לְהוֹשַׁעְנָא וְלֹא אַגְבְּהֵה לְמֵיפַק בָּהּ, שַׁרְיָא בַּהֲנָאָה.

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.