Melech in Ya'aleh Viyovoh

Question

In Ya'aleh Viyovoh the word Melech is included when we say any prayer, however in Birchat Hamozon in my siddur (Artscroll Ashkenaz) the word is bracketed and it says "On Rosh Hashana say Melech". Why is there a distinction between the version in prayers and that in Bentching?

Answer 1

The Shulchan Aruch in siman קפח seif ג rules,

צריך להזכיר בברכה שלישית א'] מלכות בית דוד, ואין להזכיר בה (ג) שום מלכות אחר. The Shulchan Aruch is saying that one cannot mention any other king in the third bracha. The Rema there comments,
הגה: וי"א דאף כשאומר יעלה ויבא, לא יסיים מלך חנון ורחום, אלא ידלג מלת מלך (אבודרהם), וסברא נכונה היא (ו) ב <ב> אבל לא ראיתי נוהגין כן. There are those who say that when one says yaaleh vyavo one should skip the word melech nd that svara is correct but I have not seen it done. This is why melech is not said in birkat hamazon because it is located in a place where one cannot mention other kings but in the bracha of avoda in tefilla there is no problem of mentioning kings and so the word melech can be in yaaleh vyavo.