Rename a ton of files is easy at the terminal (using bash scripting).. On the command line, just type something like:
Code:
for file in $(find . -name \*.jpg); do
newname=a_new${file};
mv $file $newname
done
Just set the term in find to find the files you want. See man find. Then newname should just be set to what you want the new names to be. So a${file} in the original request. You may be able to wrap this in an automator action if you need to do this often?
Disclaimer - please try this on a couple of files first and backup the directory of files before running it. I haven't tested this.