You need to do it in the same keymapfile (for the specific toon) as you done the 'follow' in, cause you can only load one keymapfile for a wow-client.
So, yes, your above example is correct (for ToonA).

Frosty descriebed a 'fast setup method' which is a modification of the original system, which i'm using, where you only have to configer the follow and assist-keys with keymaps (with the drawback, that its not 'targetfree' and you have a seperate assist-key).
So yes, it was not a direct answer to your question, only a hint, how you could speed things up...