Find all files in the current directory (and its subdirectories) and sort them numerically, then use xargs to pass each file to sed to replace any numbers with the corresponding letters (A for 0, B for 1, etc.) using the tr command.
find . -iname "*.*" | sort -n | xargs sed -i -e 's/\s*\([0-9]\+\)\s*/echo $(echo "\1" | tr "0-9" "ABCdefghijklmnopqrstuvqxyz")/goe'