Button to add the "#" sign before numbers

I have many comic book files named in a format of "Super Puppet 03.cbr" in which the title comes first, then the number, then the file extension. Ideally, I would like to use a format of "Super Puppet #003.cbr" where the issue number is always three digits long and always preceded by the number sign, "#." Is it possible to construct a button to do this?

Learned enough Regex (which still confuses the heck out of me) and did enough trial-and-error to figure it out.

Old Name: (.+)(..).cb(.)
New Name: \1#0\2.cb\3