Simple question. If I meet the conditions for an allied race on one faction, would a faction change transfer the reputation to the opposite allied race and unlock that, too?
Would it unlock both? Would it stay on the original faction? Would I switch access from one to the other? How does this work?
Yes, if you have done the unlock for an AR. This stays, you can delete all your characters and still make them.
For legion reps the reps are independent and don’t convert.
For BFA the reps convert and you can unlock as usual after meeting the requirements.
Yes. You will still have to go back and redo the war campaign though.
Ah, so what you’re saying is if I do a faction change after having unlocked the Zandalari and the Mag’har, I can then switch to Alliance, quickly breeze through their war campaign now that the reputation requirements are gone, and then unlock the Dark Iron and Kul’Tirans over the course of a day, ending up with access to all 4?
Criteria can be changed over…so say you got exalted on the rep that is the volduni equivalent on alliance side, then faction change…you would be exalted but still have to do the quests in voldun, etc. If you unlocked DI dwarves you wouldn’t automatically unlock Maghar by a faction change…
So I would end up with all 4. I just need to run through the quests.
Exactly. Lemon squeezy. 
For the kul tirans you will have to do ALL The quests in kul tiran zones. Not just one zones. Since you did all the zandalari ones it won’t mean you have the KT ones done. So will take you longer than you think
Ah, yes, the meta achievement. Good to know.
I paid a pretty penny but I did this for all the AR unlocks. It went by super fast too.
More or less, but Dark Iron will also require Motherlode and Kul Tirans will need all of the Kul Tiras dungeons.