OTOH, you could use a "while" loop. Useless example:
find <somedir> -type f -name \*.bak| while read; do
echo mv "$REPLY" "$(basename "$REPLY" .bak).abk"; done
This saves you one grep, and for the lazy, if you don't feed "read" a variable then it stuffs whatever it reads in the default var called "REPLY". Remember proper quoting is important when you (dont) expect spaces: check your script running it as "sh -x <script>" or "set -x" if you're working in the CLI.