This might be obvious, but I don’t know much about Samurai history. Toshirô Mifune’s character has different hair than almost every other man in the film. The rest of the men have very distinct shaved haircuts, but he and one other male character have nonshaved hair in buns. Does this have to do with the fact that he and the other man are samurais? Where did these haircuts for men in the Edo Period come from?
The film takes place in the late Edo era, which means the Tokugawa shogunate was firmly in place and with it was a myriad of laws and regulations for society. Hair was one of them. Styles changed for stages in people's life as well as serving to mark one's status and identity.
Yojimbo prominently features the chonmage 丁髷 hairstyle. Chon 丁 mage 髷 where mage refers to a topknot or hair bun. Chon is a reference to the punctuation mark ゝ because that's what the hair style looked like. The term used in Edo to reflect these hair variations was hanpatsu 半髪 (lit. "half hair") where the crown of the head is shaved, longer hair on the sides and back was usually tied back, and the resulting bundle flipped towards the crown. The height, angle, shape, volume of hair, etc in the hanpatsu style varied, but was conceptually the same. This would start when men hit puberty; the crown would be shaved minus the bangs, symbolizing change from child to youth. Those bangs would be cut narrower over the years until they were cut off completely, symbolizing emergence into adulthood and the ensuing era of having responsibilities.
The other hairstyle seen in the film was sohatsu 総髪 (lit. "full hair") where the main difference was an unshaven crown. That long hair would hang loosely at the nape or could be styled in a bun similar to how hanpatsu hair was worn. Individuals of specialized status such as Court nobles and doctors wore this. Elderly and sick men were also allowed to grow their hair long or, if they chose, cut it short.
The final hairstyle we see in the films is zangiri ザンギリ (kana, not ideographs). Here the crown is sometime shaved but the sides and back were cut to chin-length or shorter. The style was born from the Kyoho reforms 享保の改革 of the 1720's when the government forbade men of the hinin 非人 group (lit. "non person") from dressing their hair in the hanpatsu styles. They were also prohibited from using cords to tie back their hair. Overgrown and/or unstylized hair was a symbol of criminals and the criminal element, hence the term hinin which were outcasts.
There aren't any good resources on historic Japanese hairstyles in English that I'm aware of. For Japanese sources, you'll want to check out Edo Keppatsu-shi 江戸結髪史 (lit. "Edo hairdressing history") by Kanazawa Yasutaka. Sorry for the late reply, hope this helps!