Changing PHP configuration dynamically - php

Question

I have multiple system running on PHP 5.3 that are 15-10 years old, I can't go on those and change anything.
Problem is: some of those system are using PHP register_globals = on that is depreciate on PHP 5.3 and doesn't even exist in PHP 5.4 (http://php.net/manual/en/security.globals.php).
I am developing a new system and would like to turn PHP register_globals = off But I can't because all those old system that NEEDS it.
So I thought about dynamically changing the register_globals to off in my script using string ini_set ( string $varname , string $newvalue ) but the documentation (http://php.net/manual/en/function.ini-set.php) baffles me a bit:
Sets the value of the given configuration option. The configuration option will keep this new value during the script's execution, and will be restored at the script's ending.
Does that mean that if I have two script running at the same time lets say... One of my old system that really needs register_globals = on and my new system that use ini_set() to register_globals = off that the old script will be running with the newly changed setting? Or will it keep the setting in my PHP.ini file and the new system will run on the ini_set() configuration?
--EDIT--
After some test (see code below) #Jacob was right and it seems PHP create a context for each script and that ini_set() only change the configuration of the script its in.
TestWithIni_Set.php
<?php
ini_set('register_globals', '0');
$i = 0;
while(true)
{
if($i == 0)
{
phpinfo();
}
$i++;
}
?>
TestWithoutIni_Set.php
<?php
phpinfo();
?>
So I ran TestWithIni_Set.php first, then will TestWithIni_Set.php was executing (the infinite while loop) I ran TestWithoutIni_Set.php.
Unfortunatly, it seams like I can't change register_globals value with ini_set(). I tried the following:
//Knowing that ini_set() parameters are strings I tried those anyway.
ini_set('register_globals', '0');
ini_set('register_globals', 0);
ini_set('register_globals', 'off');
ini_set('register_globals', 'Off');
ini_set('register_globals', false);
ini_set('register_globals', 'false');
Then to make sure I didn't had something wrong in my code I tried:
ini_set('log_errors', '0');
Just to see if it would work and it did. Then value of log_errors for the script with ini_set() was off and the value of log_errors for the script without ini_set() was on.
But now I have a different problem.
How can I change the value of register_globals for only the running script if I can't change it using ini_set()?

Answer 1

I added a .user.ini file to my new system dir with the only line being register_globals=off.
I also went and uncomment the following line in my PHP.ini file:
user_ini.filename = ".user.ini"
I also made sure only a local user had the rights to make changes to that dir. So somebody couldn't go and upload a new user define .ini file for my server within this dir.
For exemple: IIS user can only read the file in this dir and can't add/modify/remove any file.