I realise now I have tried it that you can make it editable at design time.

The textual version of the tree you see in your resource is simply showing you the elements of the tree (quite why it chose to show it as text descriptions rather than the real thing is anybody's guess) - you cannot change this. By double-clicking this outline you can change the tree styles on the Styles tab.

The only way to add code for handling clicks and double-clicks, etc., is with Class Wizard. Select the ID of the tree on the left, and the various NM_ and TVN_ messages come up on the right. You need to add handlers for these just like you would add a handler for COMMAND for the ID of a button. This creates a skeleton routine to handle the event, providing the tree view structure pointers you need. All you have to do (after a visit to the help file for the particular NM_ or TVN_ message you are working on) is use the members of those structures to manipulate the tree. It isn't really that much code.

As for what appears on the dialogue resource template, I'm afraid that apart from changing the tree's basic style when it is created at run time, there is nothing you can do. You've got all that Microsoft are going to give you.