"The man changed the subject."
Translation:Mężczyzna zmienił temat.
It could but it would make a little sense here. Przedmiot means a thing or an object in general. This word can be used as subject of the conversation, lecture etc (przedmiot rozmowy, wykładu etc) but it's way more common to use temat in most cases.
Generally, "człowiek" can be an equivalent of "mężczyzna" if the sentence is about one specific man. Apart from what we have here (as of course "the man" is about one specific man), because "the" does not have any translation, and we'd arrive at "Człowiek zmienił temat" - which sounds like from a science-fiction or a fantasy movie, contrasting the "human" with other races.
We could interpret "the" as "this" and translate it to "ten człowiek", then it would be fine.