The purpose of this post is to catalog documented changes made to Hyjal and BT to determine if a “pre-nerf” option is actually unnecessary as stated by the blue in the Community Council forums here: [BCC] Why not pre-nerf Phase 3 PVE content?
Any additions to this post or patch notes I may have missed are greatly appreciated. I have not included notes with changes that are clearly bug fixes like bosses despawning during RP etc.
World of Warcraft Client Patch 2.1.3 (07/10/2007)
Black Temple
It is no longer possible to engage the Shade of Akama without completing phase 1 of the encounter.
Ashtongue Spiritbinders may now cast heals on Ashtongue Sorcerors, Channelers, and the Shade of Akama.
The Illidan Stormrage fight encounter has received additional tuning and improvements.
Caverns of Time: Mount Hyjal
The number of preliminary waves before each boss in the Caverns of Time: Battle for Mount Hyjal event has been reduced from 12 to 8, and some of the larger waves have fewer creatures than before.
World of Warcraft Client Patch 2.2.0 (09/25/2007)
Black Temple
Saber Lash tanks will no longer be knocked back by Sinister Beam or hit by Fatal Attraction, even if they dodge or parry the attack.
Mother Shahraz will now pick a new beam to cast after every 3rd beam instead of after every 5th. This means she is much less likely to cast the same beam many times in a row.
Fatal Attraction now deals 750 damage on the first tick, 1500 on the second, 2250 on the third, and 3000 on all subsequent ticks.
Prismatic Shield is now more fun. Specifically, Mother Shahraz now takes bonus damage from one school when she is resistant to its opposite. Her resistances now change randomly every 15 seconds and are capped at 25%.
Caverns of Time- Battle of Mount Hyjal
Faction and loot rewards has been added to non-boss mobs in the Battle of Mount Hyjal raid event. The faction awarded by bosses has been decreased to balance this.
The health of Jaina and Thrall have been increased again from their temporarily lowered values. They should be able to absorb quite a bit more incidental damage during the event.
Archimonde has received several adjustments and fixes to prevent some of the harder to counter combinations of his abilities. Archimonde's Soul Charge silence has been lowered in duration to 4 seconds, and the death of the Priest with Spirit of Redemption will no longer create two Soul Charges. The casting time of Archimonde's fear has been increased to 1.5 seconds, and he should now use his Fear ability on a much more consistent interval. Archimonde will also no longer cast Grip of the Legion on very far away targets.
Archimonde will no longer cast Grip of the Legion on targets that have just been hit with Air Burst.
World of Warcraft Client Patch 2.4.0 (2008-03-25)
Caverns of Time: Mount Hyjal
Azgalor's Rain of Fire now affects a smaller area.
TL;DR There are a few nerfs to Hyjal but they seem so few and far between that they decided not to go with their original versions and release 1 copy of the content. What I prefer happens is they release 1 version of the content with these changes reverted.