Is it possible to limit the CPU power for a php script through cmd?

Question

cmd/bat

Something like:
php script.php cpu max 5%

Answer 1

What you wrote is the command line parameters of php itself and have nothing to do with cmd. Please refer to the php documentation.
In cmd, look at setting the process priority with the command start:

LOW Run application with IDLE priority.
BELOWNORMAL Run application with priority class BELOWNORMAL