Older PAC systems do not have the firewall but you can change the Port for access (PACManager). This adds additional layers to prevent your scenario of downloading a new configuration or you could lock up the controller from access via PACControl. Just saw @Beno comment as I was about sent this comment.
As I noted we setup the “outside” connection which prevents PACControl Access but the internal “protected” network would allow changes and modifications. Protection can be limited access network, smart switches, etc. This is the preferred setup for both PAC and EPIC.
Physical isolation is your best protection. We often setup the primary network as an Isolated Network for peer to peer communications (EPIC and PAC), local (at the panel level) operator interfaces for plant operations. The secondary network is setup with remote Operator Interfaces, Internet Connection, etc. (on EPIC firewall setting to limit access for PACControl, etc.)
Remember on any TCP/IP system, all you need to do is add a duplicate IP address to screw up communications. This is why utilizing a smart switch is recommended if you are looking for added layers of protection, limited access, etc.
No perfect scenario but having a protected isolated network is cleanest and most secure to allow modifications via PACControl with the secondary Ethernet Connection (assuming open) setup for limited access (allow Groov View, MQTT, etc.)