I think you're taking things out of context or intentionally misrepresenting them. In the same way that wildhammer dwarves customization are available to players so they can RP they are playing as a wildhammer
but that does not equal out to trying to say 'in lore, wildhammer dwarves have sworn fealty to bronzebeards hence wearing their heritage armor'.
You're taking a player customization option and talking as if in-game lore has been changed. There is no in-game lore of a 'Horde High Elf' that's simply a Blood Elf. They're all Blood Elves and identify themselves as Blood Elves - even if there are now some with blue eyes.
There is no such lore development of a neutral High Elf or Alliance-aligned High Elf going back to Silvermoon to join the Blood Elves, let alone calling themselves 'Horde High Elf'.
So I'm not really sure what you're trying to get at really and I am more apt to agree with MyWholeLifeIsThunder that if you're talking about Blood Elves/Horde 'High Elves' you may as well simply keep it in whatever blood elf thread there is that others here are referring to.
Let me repeat:
There is no such thing in lore as of this moment that a self-identifying High Elf of neutral or Alliance standing recently (as in the inception of WoW) went and joined the Horde. Any High Elf that swore allegiance to the Horde was already identifying as a Blood Elf. Only Blood Elves are allied with the Horde. Whether they have blue eyes or not.
A player customization being available doesn't need lore explanation (as nice as it would be), and a player customization being available does not mean the in-universe lore has changed to accept it until we get actual development of it.
Case in point -> Wildhammer Dwarves as a customization doesn't mean every single WH clan has now sworn fealty to Bronzebeard Dwarf Kingdom. Sand Trolls as a customization does not mean Sand Trolls we fought are now allied with the Darkspear tribe.
Hell, Dark Troll customization does not overwrite that https://wowpedia.fandom.com/wiki/Speaker_Ik%27nal this NPC is still the sole surviving Dark Troll in existence (as of BFA!).
You are welcome to RP your own characters as such or accept others' RP of their characters as such, that has nothing to do with the game's canon for its races where they stand now until it actually becomes canonized either in-game or through game-related media from the WoW devs themselves.