Seeing as the Torah in Devarim 14:1, prohibits even a Yisrael from making a bald patch over a diseased person, why does the Torah here present the Isur by Kohanim?
Rashi (citing Kidushin 36a): The Torah does not mention "b'Rosham" about a Yisrael, nor "Al Mes" about a Kohen, and we learn from a Gezeirah Shavah "Karachah-Karachah" that what is written about one applies to the other 1 - and both are confined to where it is done as a sign of mourning for a deceased relative.
Ramban (in Devarim 14:1): The Torah here forbids the Kohanim to make bald patches and cuts because they are holy to Hashem. 2 In Devarim, it adds an Isur that applies to all Yisrael of making cuts and bald patches 3 over their deceased relatives because they too are holy to Hashem, and it is not befitting to do so. 4
Seforno: Even though the Torah specifically permits them to render themselves Tamei in honor of their relatives, they are not permitted to extend that Kavod by making bald patches and cutting themselves in their honor.
Ibn Ezra: Kohanim are warned 5 not to make bald patches, shave the beard or wound themselves, for it is not proper to serve Hashem in such a state.
Moshav Zekenim: "Yikrechu" is written with a Hei at the end (in place of a Vov), to obligate one who makes five bald patches at once, for each one.
Ramban: Because cuts on their skin and bald patches on their heads render their Avodah invalid (See R. Chavel's notes).
It is not clear why the Torah there reverses the order.
I.e. this is why the Torah put a second Isur on Kohanim. (PF) Moshav Zekenim explains that this is why only men are commanded.
Seeing as the Torah (19:27) prohibits even a Yisrael from shaving off his beard, why does the Torah here present the Isur by Kohanim?
Rashi: The Torah mentions "Lo Sashchis" 1 by a Yisrael and "Lo Yegaleichu" 2 by a Kohen - from which we learn (Riva - through a Gezeirah Shavah "Pe'as-Pe'as" that one is Chayav only if he shaves using a razor, 3 which destroys the hair down to the roots.
Refer to 21:5:1:4.
Seeing as the Torah (19:28) prohibits even a Yisrael from making cuts over a diseased person, why does the Torah here present the Isur by Kohanim?
Rashi (from Makos 20b): Because the Pasuk in Kedoshim writes "v'Seret la'Nefesh ... ", implying that for making five cuts over one deceased person one is Chayav only one set of lashes, the Torah inserts here the extra word "Sarates", to sentence the sinner to a set of lashes for each cut.
Refer to 21:5:1:4.