A family of Microsoft word processing software products for creating web, email, and print documents.
Word doesn't track changes within a SmartArt object (such as adding/deleting shapes or modifying text).
About the only thing you can do is make a copy of the SmartArt, paste it somewhere, make the changes in the copy, and then copy/paste the modified object to replace the original. Word will track the fact that the original object was replaced, but not the individual changes inside the object.