What is a textual change?

A change in the text -- the results of revision or editing. Here's a page from a book in Google Books that uses the term:

http://books.google.com/books?id=So57xdlGPuIC&pg=PA177&lpg=PA177&dq=textual+change&source=web&ots=Pl1mwyRYq-&sig=X-JwNiIhrehayj5cucX0EL34zyo

Note the difference (in the context above: state constitutions) between textual change (actual changes in the words and punctuation) and changes by interpretation, in which the text remains unchanged, but people "see" things differently.