Cutting hair and nails on Rosh Chodesh:
When Rosh Chodesh falls on Erev Shabbos: Even when Rosh Chodesh falls on Erev Shabbos some communities are accustomed not to cut their hair in honor of Shabbos due to the above warning of danger of Rav Yehuda Hachassid. [See Q&A regarding cutting nails!].
May one cut his nail when Rosh Chodesh falls on Erev Shabbos?
Some Poskim rule it is permitted to do so and so is implied from Admur. However there are Poskim which are stringent in this. [Practically one who cuts his nails on every Erev Shabbos may be lenient to do so also on Erev Shabbos Rosh Chodesh. Likewise one with very long nails may be lenient to cut them.]
If Rosh Chodesh falls on the day of one’s Mikveh night should the nails be cut prior to Rosh Chodesh?
May a woman shave her legs and the like on Rosh Chodesh?
If one began cutting his nails or hair and then remembered that it is Rosh Chodesh may he finish them off?
If one already began cutting his nails [or hair], then he may continue to cut the remainder, and Hashem will protect him of his mistake. This applies even if he began cutting a small part of the nail.
 Tzavas Rav Yehudah Hachasid 48 [hair] 49 [nails] brought in: Olas Shabbos 260/1; M”A 260/1 and Admur 260/1 regarding [only] hair; Beir Heiytiv 260/2 [regarding hair and nails]; Kneses Hagedola 260 regarding hair.
 Kneses Hagedola ibid writes “forbidden”, however the wording in Rav Yehuda Hachassid ibid and Bier Heiytiv is “One may not”; In Admur ibid the wording is simply that “Some places are accustomed” however this is referring to Erev Shabbos and not to every Rosh Chodesh.
 See Q&A regarding women shaving.
 Rav Yehuda Hachassid 49; Beir Heiytiv ibid; omitted from Admur ibid; Kneses Hagedola ibid; M”A ibid; The Ketzos Hashulchan 73 footnote 4 questions why no mention of this is made by the M”A or Admur in 260/1. See however Shaar Hakolel in Nesiv Hachaim 48/3; Shivim Temarim 57 which explain Admur omitted it because on Erev Shabbos it is Mitzvah to cut the nails even when it coincides with Rosh Chodesh. However on a non-Erev Shabbos Rosh Chodesh he would agree that one may not cut the nails. See next!
 The reason: As Rav Yehudah Hachasid warned that doing so involves danger. [Admur ibid; Beir Heiytiv ibid]
The night of Rosh Chodesh: See Ashel Avraham Butchach Tinyana 417 that the night of Rosh Chodesh is more lenient in this regard of cutting nails.
 Admur 260/1; Kneses Hagedola 260; M”A 260; Beir Heiytiv 260/2
Other Opinions: Some Poskim rule it is permitted to cut one’s hair in honor of Shabbos even if Erev Shabbos is Rosh Chodesh, as one who fulfills a Mitzvah will know no harm. [Tehila Ledavid 260/1]
 Tehila Ledavid 260/1; Shaar Hakolel in Nesiv Hachaim 48/3; Shivim Temarim 57 as is the simple implication of the Kneses Hagedola ibid; Beir Heiytiv ibid; M”A and Admur ibid which omit the custom to avoid cutting nails when mentioning the custom to avoid cutting hair on Erev Shabbos Rosh Chodesh; opinions brought in footnotes on the Tzavah ibid; See Kitzur Hilchos Shabbos-Supplements.
The reason: If Rosh Chodesh falls on Erev Shabbos, although some have the custom not to cut their hair, despite the fact that this is usually a Mitzvah to do on Erev Shabbos as one is not obligated to cut his hair every Erev Shabbos. However one is allowed to cut his nails even on Erev Shabbos Rosh Chodesh as it is a Mitzvah to cut the nails on every Erev Shabbos, and one who fulfills a Mitzvah will know no harm. It seems that no such custom exists and they should therefore be cut in honor of Shabbos. [Shivim Temarim ibid]
Other opinions: The Ketzos Hashulchan 72 footnote 4 leaves the opinion of Admur on this matter in question.
 M”B 260/7; Aruch Hashulchan 260/6; Kaf Hachaim 260/12 allows only cutting the nails that stretch past the skin.
 Shivim Temarim ibid
 Kaf Hachaim ibid
 Tehila Ledavid 260/1;
 The reason: As one who does a Mitzvah will see no harm.
 Tzavas Rav Yehudah Hachasid ibid: “A person is not to shave his head or beard on Rosh Chodesh”
 Ashel Avraham Butchach 417 Tinyana; brought in Ketzos Hashulchan 73 footnote 4.