I only want to display the edit icon (pencil image) for certain file types that I know can be edited (through our webdav configured link). Otherwise I will train then to have to check out and use a locally saved working copy.
So I only want the pencil displayed for say filetypes of (.doc, .ppt, .xls)
You can replace the evaluator associated with the edit action in the actions configuration (presuming you are using 1.3).
Look at the customisation guide for examples of configuring actions. You'll have to override the definition of the edit action in your own config file and provide an evaluator implementation that only returns true if the node matches your criteria.
That confirms my thoughts. I had altered the EditDocWebDavEvaluator.java to get the behavior I want, but I like you idea better of creating a separate custom evaluator!