My aim is to express "Promethean man" and "Epimethean man" (as in the brothers Prometheus and Epimetheus) in the style of "homo sapiens" and "homo erectus".
An Essay (cristianismeijusticia) accessible as pdf uses
to contrast with homo faber, 'man as craftsman.' The phrases occur in the section marked Conclusion. The Essay is in English.
Epimetheanus, -a, -um, would equally be a regular formation of a 2nd conjugation adjective from a 2nd conj. noun.
In Classical Latin, the phrase 'Made from Promethean clay' Ficta Prometheo Luto, can be found in Martial Epigrams Bk 10 #39 To Lesbia. Martial uses the adjective prǒmēthēŭs, -ă, -ŭm
Sic quoque mentiris. Namque, ut tua saecula narrant,
Ficta Prometheo diceris esse luto.
In this also you are not telling the truth.For, as your age clearly tells,
You might be said to have been made from Promethean clay.
Two translations, neither very close, are posted. J A Pott and F A Wright by Archive is the more literary.
Ĕpĭmēthēŭs, -ă, -ŭm would be formed in the same way.
Prometheus exists in Latin. Promethean man is something like "a man of [the] Prometheus [kind]". So I would say you are looking for the genitive, which, according to Wiktionary, is either Promethei or Prometheos. Including "man" (as in human) in the phrase, you would have
Epimetheus seems to follow the same declension as Prometheus.