Well first of all I'm a big fan of Overgrowth! How do I know this?
Not only did I preorder as soon as I knew about it some six months ago, I all the way back to the very start of the blog archives and devoured every single entry up to the current one!

As for the other part of your question, I'm afraid I am still learning Blender myself.
In particular, it's very hard to know what kind of objects you are working on, what your workflow is, and thus at what point you might be getting stuck.

However, I will take a guess:

Already-created objects are the same as made-on-the-spot objects at the most fundamental layer: as a mesh of vertices.
If the tutorials you are referring to work at that layer, then you should be set.
Simply go into Mesh Editing mode (select the object then hit Tab on the keyboard by default) and select the parts of the mesh that you'd like to affect – in this case the ears.
It might then be useful to save this selection as a Vertex Group so you can refer to it in other modules (this is the tab with the downward-pointing-vertex-trio icon).
From there you should be able to apply whatever technique is being shown and it will then affect the ears alone, as desired...