find . -name '*.php' -not -wholename '*/Loader/Autoloader.php'
  -not -wholename '*/Application.php' -print0 |
  xargs -0 sed --regexp-extended --in-place 's/(require_once)/// 1/g'

find . -name '*.php' -not -wholename '*/Loader/Autoloader.php'
  -not -wholename '*/Application.php' -print0

find . -name '*.php' -not -name '*/Loader/Autoloader.php'
  -not -name '*/Application.php' -print0

find . -name '*.php' -not -name '*/Loader/Autoloader.php'
  -not -name '*/Application.php' -print0 |  xargs -0 sed --regexp-extended --in-place 's/(require_once)/// 1/g'

$ sed -i -e '' -
sed: can't read -: No such file or directory

find . -type f -name '*.php'
    ! -path '.*/Loader/Autoloader.php'
    ! -name 'Application.php'
    -exec sed -i 's/require_once/// &/' {} +