Installing additional programs?

I’d like to install an additional program on a miab system (don’t worry, I’m not attempting to make the miab do anything other than act as a mail server and the program won’t interfere with any of the other programs). I understand that updating miab will overwrite or modify certain locations. Are there any locations in the file system that are safe? Can I open up the firewall for 1 outbound port?
For the curious, I would like to install a Splunk Universal Forwarder to send logs to a Splunk server and to run certain scripts that pull information from the server.

I want to say that would work, test it and find out. It is of course unsupported.

Yes you can open the firewall for 1 outbond port and you can also update the miab and it can be downloaded from apple support but you can not overwrite certain location