Oseh Hashalom

This time of year, some of us replace the phrase "hamevarech et amo yisrael bashalom" in our prayers with "oseh hashalom".

The reason is apparently kabbalistic. According to R' Chaim Vital, the word "hashalom" has the same gematria as "Safriel" - the name of the angel who records people in the book of life. Thus "oseh hashalom" alludes to the special character of the day.

(I find this explanation reasonable because "oseh hashalom" adds little to the meaning of "hamevarech et amo yisrael bashalom", and in fact takes away the reference to Israel. Thus at face value it is hardly an enhancement to the text. The only possible gain is in the gematria. Furthermore, the gematria would also explain the shift from "shalom" to "hashalom" in kaddish.)

I should perhaps mention that I personally do not say "oseh hashalom" in shemoneh esreh, though I might say it in kaddish.

(Source)