How to rename a certain prefix in multiple files?
You can use the following command:
find -name "*-old-*" -exec rename 's/-old-/-new-/' {} \;
This searches for files containing -old- recursively beginning in your current directory and renames them by replacing the -old- with -new-.
Note: replacing old may be enough, but I included the - in case, there is a second old in the name (like my-old-Folders.doc).