Seeking insights to streamline workflow in Storyline: Bulk triggers and Slide resets

You can't apply a trigger to multiple slides at the same time. However, the example you provided can be done another way: set the Player's navigation to Restricted. 

Here’s how Restricted navigation works:

• Storyline puts the Next button in the Disabled state when the user first visits the slide.
• Storyline changes Next to the Normal state when the slide’s timeline ends. Simply adjust the timeline to adjust when Next will be enabled.
• Next remains in the Normal state whenever the user revisits a completed slide.
• This works even if you don’t show the built-in Menu.
• If you do show the built-in Menu, users will be able to click the Menu to jump to any previously view slide. But they won’t be able to click the Menu to advance to a new slide.

You can adjust some functions for multiple slides by selecting them in STORYVIEW, and then adjusting Slide Properties.