One approach I love is turning the clan structure upside down. Instead of basing everything on environment, tie your clans to a central, supernatural resource. Imagine a world where the warrior code stems from a pact with ancient spirits of the hunt, and the clans are actually guardians of different aspects of a single, massive forest's magic. The ThunderClan analog could be Wardens of the Root, fiercely territorial over their sacred groves, while a ShadowClan equivalent are Weavers who navigate the spirit realm through dreams, considered untrustworthy because their loyalty is to balance, not borders.
You'd get immediate, built-in conflict from that. Their codes of honor would diverge wildly; what's noble to one is blasphemy to another. A prophecy plot wouldn't be about a chosen one saving everyone, but maybe about a cat who can speak to all the spirits, threatening the very separation the clans believe keeps them safe. It lets you explore themes of dogma versus truth without just re-skinning the original factions. I've seen a few fics try elemental clans, but grounding it in a singular, contested mystical source feels fresher to me.