Laws that are Applicable Between Sh'moneh Esrei and "Yih'yu L'Ratzon". Containing 3 S'ifim:
If one is inclined to interrupt [one's prayer] to respond to Kaddish or K'dusha between [the end of] Sh'moneh Esrei and "Yih'yu L'Ratzon" ["May it be acceptable"], one does not interrupt; for "Yih'yu L'Ratzon" is included in the [Sh'moneh Esrei] prayer. But between "Yih'yu L'Ratzon" and the rest of the supplications [that are said afterwards], it is fine [to interrupt]. Gloss: And this is specifically in a place where it is practiced to say "Yih'yu L'Ratzon" immediately after the [Sh'moneh Esrei] prayer. But in a place where they practice by saying supplications before "Yih'yu L'Ratzon", one may interrupt also for Kaddish and K'dusha. And in these places, it is practiced to interrupt in "Elokai, Netzor" ["My God, guard"], before "Yih'yu L'Ratzon". And therefore, we interrupt also for K'dusha, Kaddish, and Bar'khu. [His own words, following to the Rashba that was brought by the Beit Yosef]One who was accustomed to say supplications after his [Sh'moneh Esrei] prayer - if the prayer leader began to order [i.e. recite] his [repetition of the] prayer and reached Kaddish or K'dusha, one should truncate [one's supplications] and stand up. And if one did not truncate [one's supplications], one may interrupt in the same way that one interrupts in a blessing of the Recitation of the Sh'ma; even in the middle of [one's recitation].
It is not proper to say supplications before "Yih'yu L'Ratzon", rather, after the completion of the Shemoneh Esrei, one immediately says "Yih'yu L'Ratzon", and if one wants to go back and say it another time after the supplications, the permission [to do so] is in one's hands.
One who is accustomed to say these 4 things will merit to greet "the face" of the Shechina: "Act for the sake of Your Name. Act for the sake of Your right hand. Act for the sake of Your Torah. Act for the sake of Your holiness."