You can have My Tokens in any Folder and the sub folders and programs inherit the my token.
If you modify that token at the child level, it becomes overridden at the child level only.
I've done the multiple webinar before and it's not super hard, but takes some thought.
Usually I recommend a campaign to call the registration flow within each webinar Program, so that the main registraton page lives in a separate program at the top.
You may need a separate "Webinar Date Code" field to make this work.