I'm pretty positive that program tokens are exclusive to the programs they live in. Here's a list of the token glossary for the system-wide tokens: https://community.marketo.com/MarketoArticle?id=kA050000000LBvaCAG -- so unfortunately, I don't think you'll be able to achieve that.
I am not sure if this would help you, but I recently created a single landing page with a single form which allows you to register for any of 11 webinars. The way this worked was to create a form which used tokens as drop down selections, create a "master" form fill registration campaign containing token values, and use that registration campaign to pass registrations to each individual webinar based on the value of the token. You could do this with actual dates or tokens. I liked the token approach because I will be able to easily reuse the same form again in the future.
The token used for the drop down selector passes the selection to a custom marketo field I called "webinar session" and the token value is the date. Here's the landing page:
It's working pretty well so far. I imagine you could use a custom field to contain a value for true/false is "register for all" and add people to all webinars this way. You might want to turn off the auto-confirmations for the webinars though or people will get a slew of registration confirmations all at once. Not sure if you'd want that.
Not sure if possible to pull tokens from Program to Program, but what if you did a workaround like create tokens at the Folder level? Then all programs within that folder would inherit said tokens.
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.