I think I might have a better solution. I'm pretty sure you want a naming system where the player is allowed to input any name they want, but if they input a specific name like, "Dummy", they get a different response. I actually learned how to do this recently!
First, go into the Event Commands and find Name Input Processing. Input the actor who's getting named, either your main character, or even someone else, and give your player as many available characters as you see fit, as long as it's as many or more than the name you already gave them.
Now that you've done that, go to Event Commands again and find Conditional Branch. Go to the Second tab and input the actor who's name is getting changed or given. Now go to Name and input the name that will change the dialogue, ex. 'Dummy". Make sure you keep in mind any spaces and capitalization's will have to be replicated exactly for the name to be recognized. For example, if someone typed "dummy" and you put in "Dummy' with a capital "D" it wouldn't work. Now, if you want the character to receive the chosen name, just go to Event Commands again, find Change Actor Name, and select the actor whos name is getting and change it!
Now, just type in whatever dialog you want to happen when the chosen name is invoked! In the Else area, put in whatever dialog would have occurred if they had been given any other name. I like to use this for jokes like if people try to put profanity as the characters name, but you can use this for a whole bunch of cool ideas and puzzles.
I hope this helped, good luck on whatever you're working on!