Just doing a quick repost of the Q&A about Anim Lib in the 2D Toolkit thread on the Unity Forums in case people look for the solution over here:
Question was: How to swap "Anim Lib" with code.
Keep in mind that you should have the new animated sprite in a "resources" folder
sprite = GetComponent<tk2dAnimatedSprite>();
sprite.anim = (tk2dSpriteAnimation)Resources.Load ("new_anim_sprite_name", typeof(tk2dSpriteAnimation));