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:
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.