regex replace multi-line + in multiple files

gistfile1.txt

$FILES="*.rs"
$REGEX="s#(.*)\n(.*)/\2\n\1/"

find . -name "$FILES" | xargs perl -0777 -pi -e '$REGEX'

# flag: -0777 tells perl to read the file as a whole
# replace '-pi' with '-pi.bak' to create backups