The MB brings that the Gra says that the chazzan should indeed say “yiheyu l’ratzon” at the end of chazaras hashatz. Rav Malinowitz adds that if one does so, care should be taken to say the words carefully, not to slur or swallow them.
Shabbos Bulletin Parshas Shelach Lecha 5778
About the Author: Lev Seltzer
Lev Seltzer has been a member of Beis Tefillah from just a short time after its founding. He currently manages the BTYA.org website, and can be found every morning in the BTYA "Vasikin Room" where he is the gabbai of the minyon.