Extend blocks with a field via PHP code

The CMS Questions
1

Is there a way to extend blocks with a field via PHP code, i.e. with a custom plugin in the backend? I would like to integrate a toggler in every block.

I don’t want to copy all yml and add them as a group field.

2

You can create PHP-based blueprints: PHP-based blueprints | Kirby CMS

For your use case reusing/extending a single field might still be an option: Reusing & extending blueprints | Kirby CMS