Based solely on experience with alarms of this period (i.e. guessing) - the “wired commands interface” is probably a serial RS232 port, which would allow an external system to interrogate and control the alarm. Really useful!
But sadly, unless you can get the manufacturer’s specification for the data protocol used, not much chance of exploiting that. As a security system, that is likely been made deliberately difficult.
One approach might be to find out if there is a PC application around that will talk to the alarm. You could then monitor the data traffic and figure out essential commands and data. Very tedious!
I would guess again, that the RJ45 socket is another way to the same serial port, perhaps an RS485 version. It’s not likely to be a LAN port, that would usually be an add-on option.
I don’t think you’ll be able to remotely set or unset this alarm system without this knowledge. However - if you have the installer’s manual it might describe how to control the alarm from a keyswitch instead of keypad. Such a keyswitch could be simulated by a relay under OpenHAB control.
As sihui says, there are many ways to connect two binary sensors for alarm on/off and alarm normal/ringing indication (and possible relay for alarm enable/disable). You might want to decide how your home system might develop in the future, to help choose a suitable technology here - zwave, KNX, WiFi ESP, blah.