Rename files (with RegEx) and Keyboard Maestro
This is a Keyboard Maestro macro which gives you a prompt for every file you have selected in Finder and optionally allows you to rename the file with a regular expression.
It re-uses the last regular expression so you can apply it to more files.
Slightly modified you can rename a bunch of files at once.
The prompt gives you two text fields.
One for the new filename (excluding the extension) and one for the optional Regular Expression. If the Regular Expression field is empty, no RegEx replacement takes place.
This macros asks for all files one by one.