Board Thread:Spoilers!/@comment-24663542-20150216235529/@comment-1894786-20150219214636

When it comes to recasting, as far as I know, the only characters to be recast are:

Sean Maguire as Robin Hood, taking over for Tom Ellis (who couldn't continue the character due to scheduling conflicts)

Merrin Dungey as Ursula, taking over for Yvette Nicole Brown (who couldn't continue the character due to caring for her ill father)

And if it turns out that Ana is in fact Anastasia Tremaine, both her and her mother would've been recast, as uncredited actresses played them in "The Price Of Gold" during a short cameo (same with Georgina and Elsa, who was played by an unknown actress in "There's No Place Like Home") and then Jennifer Koenig playing Cora in her debut episode "Hat Trick" (but Barbara Hershey herself voiced Cora in this episode, so it doesn't really count...)

With Ursula, it can easily be explained away as Ursula having a different voice when she possesses a statue (as long as they don't have Merrin do it). With Robin, the only logical explanation is a glamour spell that turned Sean into Tom temporarily. Emma and Hook's glamour spells (and Regina/Wilma's) didn't disappear until Rumple forcefully shut them off, so it stands to reason that glamour spells are semi-permanent.