I think it's easy I can script it if needed ...
Go ahead, good luck!
How the script is supposed to be created ? I mean how the script will recognize that a graffiti was placed on another graffiti?
It is possible. I could do that myself but will wait for a developer to add a custom event for me ideally as I don't have access to graffiti script. The question I want to ask is, what currently happens whenever you spray a graffiti over another graffiti?