This year the EHC decided that the following clause would be used for Grandfathering spell changes from the council meeting:
"...all characters that had spells which were changed at this year's EHC may change the spells such affected at the first event they play..."
Based upon this, the following is the list of spells that I believe were changed significantly enough that they warrant being able to be grandfathered by spellcasters that currently know them:
Animate Limb (new name, bonus when cast on controlled undead)
Assassin's Blade (gained Eviscerate)
Circle of Protection (bigger rope)
Create Poison (gained Poison Weapon)
Enchant Blade (gained Silver Strike)
Familiar (removed 5th circle options)
Implement (book/tome, removed redundant option)
Magic Missile (clarification)
Quicksilver Armor (removed)
Poison Weapon (moved into Create Poison)
Silver Strike (moved into Enchant Blade)
This is a pretty conservative list, and does not include spells that only had minor changes such as a name or editorial change. I also removed spells that were affected by a systemic mechanic change or clarification such as the Item Mechanic change and the requirement of Verbal Components to be written.
I decided that my list would be conservative as learning spells has become quite fast with people often learning a full path of spells in a single event, and I have even heard of people learning two paths of spells at some of the larger events of the year.
Keep in mind that the Magic Marshal or Event Holder of the first event you attend may have their own decision on what spells can be grandfathered and these are my own thoughts and what I will be doing if I am Grandfathering anyone.