If you could alter a major part of lore...

[Destil]

I would kill Aggra so Thrall would remain the Horde Chieftain.

I would replace Aggra with someone who doesn't sound like they have a Smoker's Lung.

And have Deathwing's development be much better, and not have him die in an explosion of glitter..

[TheWindWalker]

If we're talking even something as drastic as "frozen time events" (like in Chrono Trigger after the big climax), I'd reach out and rescue Broxigar and drop him off on the Echo Isles just days before the raid on Orgrimmar. Can you imagine the shock of having him walk in just after you've brought Garrosh to a point that he'd call enough reinforcements to force the heroes in a losing battle?

[hiragana]

Destroy the titans. Then we can all play as different old god factions .

[Thassarian]

Change Uther's story to be one of a strict teacher who takes no shit. Prevents the Stratholme Purge, prevents the Lich King coming to power. Scarlet Crusade and the Argent Dawn never exist, the Order of the Silver Hand is at full strength with both Mograines, Tirion, Arthas, Uther and so on.
Remove Wrathion, put Sabellian in the same position (Sabellian > Wrathion. Hoping Blizz do something fairly interesting regarding the Black Prince and the Heir of the Blackdragonflight when they eventually come to know of each other's existence).
If not the first one, Have Darion and Tirion act upon their doubts regarding Sylvannus. Have her removed and put whoever the freshest corpse is as Leader. If any leader needs killing off, it needs to be her.

[Dreknar20]

I would crush the Skull of Gul'dan before Illidan got his hands on it & prevent him from being the Demon he became.

but Illadin taking the Skull allowed him to deal a major blow to the Legion.......

[Stir]

One thing?
Prevent the initial clash between the Warsong and the Silverwing Sentinels.

[Ryuji]

Saw someone post it on the first page, but have some bosses defeated instead of killed like they were. Redeem them and whatnot. Illidan and Kael stick out the most in my head atm.

[nnelson54]

Make the Broken the player race and undo everything TBC did to the Draenei. It was such a huge let down when the Draenei were announced and I was looking forward to playing a bad ass Broken, then they completely destroyed the lore surrounding them and turned them into space goats for no reason other than they wanted an excuse to make them look prettier.

[Tenhou]

I'd probably warn Aegwynn ahead of time of Sargeras plans to possess her son.

Why? To see if Medivh perhaps could be born with his own will from the start and see how that would change the whole thing with guardians of tirisfal etc. Always liked the lore surrounding Aegwynn and Medivh, and would love to see how it'd go without Sargeras interference.

[Precursor]

I would honestly remove tedrasill from lore all together, it was like 10 years and it became a tree/stump with anicent buildings on it. I dislike it unless they actually one day changed it to a giant tree one day. But if i had the power i would remove that idea from the night elfs head and force them to build a new city in a subzone of ashenvale or some run off from mount hyjal.

I would also create some sort of quest line twist in eastern questline where you head so far into the scourge teritory and you end up surrounded, then all their eyes glow orange and they bow to you then proceed to creep away back into the forest. Just something to let us know that bolvar is infact controlling them now.

[IrishDK]

Not EXACTLY lore related, more gameplay, but The corrupted Ashbringer was just left at a loose end....

OT:No pandas, illidan, kael and arthas <3

[Pebrocks The Warlock]

OT:No pandas, illidan, kael and arthas <3

So basically you want to get rid of WC3 and in doing so WoW?

[nnelson54]

So basically you want to get rid of WC3 and in doing so WoW?

For bonus points, he played a DK. No Arthas means no modern day DKs.

And the Corrupted Ashbringer wasn't really left a loose end. The lore behind it was retconned at WotLK's release but it's story has very much been completed.

[Faithshield]

If I was to change Warcraft Lore, I would probably stop the Night Elves allying up with the Alliance and instead make them Ally up with the Tauren much more firmly and in the process broker a ceasefire with the Orcs/Trolls.

The Forsaken would take a much more redeemed path with Sylvanas; allying back up with her once comrades the Elves of Silvermoon, and both would rejoin the ranks of the Alliance for a unified Eastern Kingdoms.

Draenei would be replaced by Furbolgs and be much more closely linked to Night Elves. Goblins and Worgen would stay as they are now, allied to the Horde and Alliance respectively.

I'm not sure how a Kalimdor vs EK WoW would have turned out, but thats not for me to consider right now :P

Thrall and Jaina storyline would also have developed differently.

[wimbo125]

Save Mograine from Undeath, thus saving Uther and no Forsaken, yeah!

[Stormdash]

I'd kill Dar'Khan Drathir before he could sell Quel'Thalas to Arthas, leaving the still Kel'Thuzad-less Scourge stalled in its march to the Sunwell. Perhaps a long enough standoff to let Stormwind, Dalaran, Ironforge, et al come to their aid and wipe out Arthas' army right there near the place where it all went down hill for him, Stratholme.

-- Sunwell isn't destroyed, so the resultant fall into desperation by Kael'thas never comes (also, the only Elf Paladins would be guys like Mehlar Dawnblade).
-- no Kel'thuzad, so Naxx never comes to the Plaguelands.
-- Archimonde never summoned to Azeroth
-- Night Elf immortality never lost
-- Forsaken never arise
-- Illidan never consumes skull of Gul'dan, sparing who knows how much troubled on Draenor

I'm not sure what would have really happened in the Kalimdor side of things without Archimonde's circumstances to force the humans, night elves, and orcs to cooperate. But overall, that one very small thing could have completely averted most of the Third War, and left the Lich King as nothing but a frozen fish in a barrel in Northrend for united forces that would have still had Antonidas, Sylvanas alive, etc. The full strength of Quel'thalas and the other Grand Alliance nations marching on Northrend to return (a carefully wrapped) Frostmourne to the Lich King by shoving it up his arse.

There also never really is a new "Horde vs. Alliance war" as long as the orcs keep the peace with the humans on Kalimdor -- the Alliance kingdoms would never have likely come across the sea to go after them, and since the Night Elves never really would have been brought into the Alliance directly, the most you might have there is a ongoing conflict between the Night Elves and Horde.

[Mongoose19]

Keep Arthas alive.

[NSrm]

When Lich King dies. It never made any sense. Scourge being a bigger threat without a leader?? .. come on.. really??

[Landin55]

When Lich King dies. It never made any sense. Scourge being a bigger threat without a leader?? .. come on.. really??

Really...not that hard to understand.... it will be an army becoming a locust horde. Its not like cutting the head off a snake....more like kicking the bee hive.

[Golden Yak]

I suppose I would iron out the draenei/eredar clusterfuck that popped up during Burning Crusade, just for the sake of having things neat and tidy.

-The three eredar Kil'jaeden, Archimonde, and Velen still become the leaders of their people.
-After achieveing utopia, Kil'jaeden and his followers begin experimenting with dark magic, eventually being exiled from Argus by Archimonde and Velen.
-Kil'jaeden and his eredar wander the universe with their magic powers and eventually become demons, in time coming into contact with Sargeras (the uncorrupted) and being imprisoned along with other demons.
-When Sargeras finally goes bad, he breaks out the demons and Kil'jaeden leads him to Argus, where he corrupts Archimonde and forces Velen to flee.