I'm really glad you asked that. I've seen so many muds that take a zone, make superficial changes and replace the builder's name with the name of the person who made the changes.
I personally don't usually add my name as a builder to zones that I've adjusted but I think I'm in the minority on that. I've got nothing against putting your name as an additional builder as long as you keep the original builders in there. I "grew up" with the memory of C.A.W. Right now, you can see this story
here
.
If you wanted to see how I marked the areas I've adjusted, look at rooms 28800 and 55500 (Galaxy and Ultima).