I have two examples here where the particle の is used where I would've used が so I was hoping someone could explain if there's a difference in these instances, or if either is acceptable.
主人のいない侍
顔のない男
Is there a reason の is used in place of が/is the meaning the same if one is used over the other?
In short, relative (adjectival) clauses (that is, short phrases modifying a noun), の can replace が. There's really not much to say about it, other than that it is only used in very short clauses (usually subject の verb-or-adjective, and that's it), and if it's ambiguous with a "possessive" の than you either can't use it, or it has to "work either way".
You also wouldn't use it if there's any emphasis on the thing before が - the construction kind of makes the whole sub-phrase sound like a single adjective (I mean, that's what it is already, regardless of の vs が - but it sounds more flat with the の, I think)
Both of の and が is OK to understand above two sentence. The reason is because 侍 have 主人, and 男 have 顔(usually).
But sometimes の and が can't be used. 〇 Aさんが私に書いた地図 ✕ Aさんの私に書いた地図 →because 地図 doesn't belong to Ａさん
〇 Bさんが私にくれた時計 ✕ Bさんの私にくれた時計 →because 時計 doesn't belong to B さん
