I’ve seen a lot of different strategies for ECN documentation. – Word, pdfs and Excel are most typical. The problem is that often times it can be difficult to describe where in the part/assembly you want the change made.
Have you considered using an eDrawing as your ECN document? With eDrawings you can point right at the location you want to make the change, add a comment balloon then if you need to be even more verbose in the description field you can type to your heart’s content!
With eDrawings you can spend less time producing the ECN document and be more assured your readers know exactly what the ECN is supposed to accomplish.