If you want to make it a bit better, so it will work with any number of digits followed by a dot and a space, and so it won't accidentally strip 4 characters off a filename that doesn't start with any digits, then you can use something like this:
I would like to put this behind a button. Somehow it's not working (I know I'm doing something wrong ). I placed following line in the function box of the button:
Rename FROM REGEXP ([0-9]+.)(.*) TO REGEXP \2
When I click the button nothing happens. Any idea what's missing?