Fiddling with cultures- both real and previously imagined- for D&D is something I do on a regular basis.
In one post-apocalyptic fantasy homebrew, my Warforged are called The Inheritors. Why? Because Warforged were created by Dwarven ,aster craftsmen for a psioniclaly active race as fantasy analogs of the Cybermen or Daleks from Dr. Who. But they never delivered them to the intended clients, as both they AND the dwarves were effectively wiped out during the conflict, and the Warforged were repurposed to house psionically active Dwarves to ensure their culture would live on. So The Inheritors have a Dwarven culture.
When I imported the Seshayans into another homebrew, they were the former lords of the Underdark whose empire had been so thoroughly crushed and its people so scattered that no living memory- and few texts- recall their empire even existed.
In another script-flip, another campaign had elves who were actually crash-landed alien Greys whose technology spawned the legends of impossibly beautiful humanoids (solid-light holography) who lived in timeless Underhill (where stasis fields and other time-manipulation effects were used).
One unused campaign featured surface elves as the magic-using “evil empire” who had suppressed the other surface races and driven their drow cousins into the Underdark.
