I think here’s a good serverfault topic on the subject.
Yes it’s safe to modify these files, but they could be overwritten by a new install, so you’d be wise to write some automation around configuring your apache. Though the file /opt/rh/httpd24/root/etc/httpd/conf.modules.d/00-mpm.conf determines which type of mpm module you use (you’ve linked a CGI config file, that’s not the file/config you’re looking fo). Looks like default is prefork. If you want to switch types, then modify this file, if not, just leave it. If you’re not using any PHP modules, I’d suggest switching to mpm_event_module, otherwise stick with prefork. There are also links in this file to the actual apache documentation on all these threading modules.
Then I’d suggest dropping a brand new file into /opt/rh/httpd24/root/etc/httpd/conf.d/ like say worker.conf that won’t get overwritten and putting your worker configurations there.
Looks like prefork is the default and what you’ve got configured (from the logs given), so that element has the only values in it.
<IfModule mpm_prefork_module>
MaxRequestWorkers 512
</IfModule>
<IfModule mpm_event_module>
</IfModule>
<IfModule mpm_worker_module>
</IfModule>
If you do stick with prefork, just keep an eye on your memory when you start to top out in request workers.