Rename files using math operations

This should do the trick. If you do not want the leading zero you can remove sprintf as well as the "%03d" format string. Furthermore, if the files to be renamed will always begin with a, you can also supplant the leading regex [a-zA-Z]* with the literal character a. Lastly, although the * file specifier may be adequate, I would recommend tacking on an extension as an additional safety precaution (e.g. *.png).

As always, try it out first using the -n flag to verify the rename is correct.

rename -v 's/([a-zA-Z]*)([0-9]*)/$1.sprintf("%03d",$2+10)/e' *