Find all files in the root directory, print them out, and for each file, use sed to replace any string that matches the pattern of a valid email address with a string that matches the pattern of a valid username.
find / -type f -print0 | xargs -0 -n1 -P1 sed -Ei 's/[A-Za-z0-9_\.-]*@/\+[A-Za-z0-9_\-\.]*/g'