There is a minhag to only say Selichos before Rosh HaShanah and not during Aseres Yemei Teshuva. I know in Chabad this is in the minhag. Is this minhag practiced anywhere else? Where does it come from? What's its reason?
The Lubavitcher Rebbe (Sefer Hashichos 5750 vol. 1 page 351 footnote 132) quotes the Tzemach Tzedek's explanation of the Chabad custom to recite selichos only until Rosh Hashana and not during Aseres Yemei Teshuva:
עד כאן (עד ר"ה) - מצות אמירה, ומכאן ואילך - מצות עשייה
Until Rosh Hashana the emphasis is on speech, from then after the the emphasis is on action
The Sefer Otzar Minhagei Chabad usually attempts to compare the Chabad minhag with that of other communities. He brings (pg 162) a custom in Ger (until the Emrei Emes) to say only the first selichos, or Erev Rosh Hashana or Erev Yom Kippur, and in Chernoble a similar custom (also subsequently stopped). So it seems that at least that author couldn't find more than that. (Thanks @Yishai). See the sefer for a more comprehensive discussion on the topic.