I would probably end up having to use a contacter / relay, because I don’t think the tiny little switch in there can handle the mains.

Most of our fire alarms are designed to operate at 24V DC. Putting mains voltage through them would likely not end well .
However, some of our devices can operate on mains voltage, normally multi-purpose sounders that can be mounted on industrial machines, or similar. They should always say what voltages they can handle and what terminals you need to use for said voltages.
I have seen your pull stations. They do appear to be just light switches with a fancy plate on the front of them. The switch itself may tell you what it can take, otherwise assume it can only take the standard fire system voltage and use relays.

Another thing to keep in mind is that pull stations are a latching switch.  They are designed to mechanically lock in the on position when activated, and usually have to be opened to be reset/turned off.  Unless the latching feature can be defeated, it would make an inconvenient light switch.

I would probably remove the lock so that I could turn it off without having to use a key.