sudo chgrp -R nobody /whatever

mkdir sticky
cd sticky/
touch blub
chmod 4755 blub
ls -al blub

chgrp -R myuser .
ls -al blub

find /whatever ! -type l -perm -04000 -exec chgrp nobody {} +
                                      -exec chmod u+s {} +
find /whatever ! -type l ! -perm -04000 -exec chgrp nobody {} +

chown_preserve_sec() (
  newowner=${1?}; shift
  for file do
    perms=$(stat -Lc %a -- "$file") || continue
    cap=$(getfattr -m '^security.capability$' --dump -- "$file") || continue
    chown -- "$newowner" "$file" || continue
    [ -z "$cap" ] || printf '%sn' "$cap" | setfattr --restore=-
    chmod -- "$perms" "$file"
  done
)

chown_preseve_sec :newgroup file1 file2...

# save permissions (and ACLs). Remove the "# owner" and "# group" lines
# to prevent them being restored!
perms=$(getfacl -RPn . | grep -vE '^# (owner|group): ')
# save capabilities
cap=$(getfattr -Rhm '^security.capability$' --dump .)

chgrp -RP nobody .

# restore permissions, ACLs and capabilities
printf '%sn' "$perms" | setfacl --restore=-
[ -z  "$cap" ] || printf '%sn' "$cap" | setfattr -h --restore=-

cd /home/me
getfacl -R /whatever > whatever-permissions.org 2> /dev/null

# A) change lines starting with      # group: root
# to                                 # group: whatineed
sed 's/^# group: root/# group: whatineed/g' whatever-permissions.org > whatever-permissions.new

# B) change lines with               group::x.y
# to                                 group::xwy
# (where x, y mean: whatever was there before)
sed 's/^group::(.).(.)/group::1w2/g' whatever-permissions.new > whatever-permissions.new

cd /
setfacl --restore /home/me/whatever-permissions.new