It's a nice idea if the lanyard related only to autism.
As I understand it, the lanyard is used for any hidden disability, i.e. not just autism but things like stoma, Crohn's, etc. On the back it can be customised to give further details.
I've got one. It says 'I am autistic. I may need more time and space in certain situations. Please be patient.' I very rarely ever wear it. What it does give me is confidence that I can use it if I run into a situation where I might get overwhelmed.
I've never been to Autscape but I believe they had a traffic light badge like you describe, which can be changed by the wearer according to their needs at the time.