Answer by Shawn for Cloudlinux + CageFS + PHP Selector - how to update default php.ini for each PHP version or for each domain account?

Found the answer. For alternative PHP versions, the process is different.

After modifying /opt/alt/phpXX/etc/php.ini

Run cagefsctl --rebuild-alt-php-ini

That's it. No need to rebuild apache.

For an individual user's php.ini, check here