How to configure php.ini file settings in PHP code?

You can use ini_set() function to change the php.ini file configuration variables. init_set(variable, value);

List of possible variable can change using ini_set() function.

SMTP

smtp_port

sendmail_from

max_execution_time

display_errors

memory_limit

upload_max_filesize

max_input_time

error_reporting

etc...

For example:
ini_set('max_execution_time', 120);