I suppose a lot comes down to how much one believes the book defines their world or they define their world.
Would a GM allow a "race" to be more fluid?
Can I be a "stone elf" who is a member of elves who have the stats of dwarves, total swap, but more the appearance of elves. Not drow. Or maybe an off-shoot of drow with all the specs of dwarves.
Honestly, off the cuff, I would be fine with that.
But, unlike what seems to be a source of contention, it would be a part of the world. Folks would not be assuming "only dwarves have" trait ABC.
Just like, if I allow reskinning familiars, folks dont assume "only owls have flyby."
Imo, if a gm has an issue with flyby attack, they should fix it, up front, before they let a player choose it... not allow it but then stick it to them by disallowing reskin for funsies.
I'd work with someone who wants an elf adopted by dwarves so they can swap certain racial attributes. But if someone wants powergame, then the fluff should only go so far. If someone wants 10 foot reach, then play a bugbear if its that important. You shouldn't be able to reskin your bugbear into a pretty elf maiden.