Is it possible to use the RS-232 to run various scripts? For example, if I connect a button/switch to pins on the RS-232, can I use that to trigger a script to run?

No.

Well, short answer is NO...

... but there is a way to accomplish what you want:
Use arduino to interact with the console directly (log in, issue command, log out). Can use special account with restricted access just for what you want to do.

For more complex things it's even possible to have full access to the API this way:

• Configure PPP server on ROS, give it static IP and enable API access from that IP
• On arduino (or other platform of your choice) have PPP client that "dials in" the link to RB over serial "null modem" cable
• This way arduino can make GET/POST requests to REST API
• And you can send pretty much any commands/change anything on the router from your microcontroller

There is "PPPOSClient" library you can use (https://github.com/levkovigor/ppposclient), made for use with GSM modems, but you can easily strip all of the modem stuff and go straight to establishing PPP connection.

Short answer is "No." because if the user wanted to buy something else instead of saving money and using RS232 pins with a simple button,
he didn't even ask the question...