Look at pages 2,3, and 4 in this paper. The general outline of how to add to or alter code is here. Basically, EG will give you places where it is appropriate for you to enter your own code. If you wanted to change some -statement- within the code that EG has built, however, you'd have to go back and reselect or change your choices in the various task panes (for example you want to change AGE to HEIGHT -- but EG has already put AGE in the code that you see in the Preview Code window -- to get HEIGHT, you'd have to reopen the task and select HEIGHT instead of AGE.)
Chris also describes the tools in his "SAS for Dummies" book (which is actually a book about EGuide 4.1).
The "insert code" tools works very well. There are a few times where it hasn't had an insertion point where I needed it. If so, I would "Add as Code Template" (right click on the task to see that choice) and then edit directly. I also do that when I want to make a macro out of a task.