Thanks for your feedback!
Well it depends on the changes. If the client’s changes are extra features (for example: adding a new comment feature in a blog site), wireframing the requested feature is always a good start to better communicate the layout. Then by using the website’s style guide (that should be already designed in the first release), the prototyping shouldn’t be complex since you will be using the consistent design elements that you agreed on. However if the changes are design enhancements (for example: changing the UI of a certain element without changing its layout) then prototyping directly is necessary in this case.