I just started modding and 1.6 is the only place I know a little. I'm planning to play with the AI and if it's possible to do what I want, maybe I'll work on it.
I think you should be more specific about what are you trying to do. It's seems you're moving in something deeper in the internals and it might bug something as Draco18s said.
I've extended an EntityCreature and added a few AI tasks (as Villager). In few steps a managed to create a FollowTarget AI that makes the mob follow a PlayerEntity if it come close enough. The behavior is just the opposite of AvoidEntity AI. Btw you can pass the speed to those AI.
You may know all that, but I don't follow your problem...