It seems that many achronim say that undergarments would not need to be switched, for kavod shabbat.
- Would this include a tallis katan worn under one’s regular clothes, or is there a kiyum of kavod shabbat that is more than underwear/undershirt/sock?
- Would a tallis gadol ideally need to be switched, even though it’s just worn for tefillah and would have the same physical appearance as a tallis worn during the week?
- You are asking an interesting question. The Netziv (Emek Hanetziv Bereishis – 4) says that we learn this from two different pesukim. The outer garment are from the posuk where Naomi told Rus to put on her Shabbos dress “ושמת שמלותיך”, when she went to Boaz, and this is referring to the outer clothing, and the undergarments from the posuk “מכבדתו… שלא יהא מלבושך”, the word לבו”ש stands for לא בושה refers to undergarments, which cover a person’s nakedness. You are therefore asking, what about tzitzis which go under the outer clothing but not against the skin? Halachically we don’t have to change undergarments for Shabbos, however the ideal thing is to change all our clothing for Shabbos. (Arizal Shar Hakavanos 63a, Pri Eitz Chaim- Shar Hashabbos 4 D:H Binyon). This would include the tallis katan, (see Chazon Ish (Zachor L’dovid) pg. 330-8, Ashrei Ish O:CH 2-1-(10), Chut Shani (Shabbos) 1-chap. 3 -1.)
As a side point the poskim agree that although it is ideal to change undergarments for Shabbos, one does not have to have special undergarments for Shabbos, since they are regularly washed, it is sufficient to change to clean ones. (Piskei Teshuvos 262-4 ftnt. 30).
- Regarding Having a special tallis for Shabbos it is idea to have a differant one for Shabbos. See Magen Avrohom 262-2, Eliyahu Rabba 262- 4, M:B 5, Kitzur Shulchan Aruch 72-16, Shmias Shabbos Khilchoso 42 ftnt. 206.