Is there a way to create a unique property for 2 of the same object

I was just thinking about making a dialogue system, is there a way to make a ‘trigger’ object which can be given a unique property unique to a specific instance of said object

so that multiple of the same trigger can create different systems

I want to do this to prevent me having to create so much coding boilerplate having to either detect a certain instance of an object, or to create several different objects that fill the same role

Use a closure, with which you can do exactly what you describe, they are the best option.
See Programming in Lua : 6.1
At first they might seem complicated, they are not, they are straightforward to create use and implement.