Linux GUI Regular Expression File Renamer (with substitution)

I realize this is not exactly a "GUI", but you didn't say anything why that is a requirement, and there are already-written command-line tools that do this; e.g. perl-rename:

find ~/dir -type f -exec prename -n 's/^(\d\d)(\d\d)(\d\d)(.*)$/$3$1$2$4/' {} +

(-n turns on "test" mode. When you're satisfied with the output, run again with -v or no options instead.)

Some good GUI tools for renaming files are

• KRename for KDE desktop environment (I personally prefer this one because I'm a KDE user);
• GPRename and pyRenamer for Gnome.