P: Flip Horizontal Shortcut for a FILM scan editor

"I wish there was a shortcut so i can sync this setting from one to dozens of images at a time."

As pointed out by Per, you can use the plugin to assign a shortcut to Flip Horizontal. But that doesn't address the rest of your implied question, which is how to sync a flip to dozens of images at the same time.

To sync that change, you don't need a shortcut. Rather, do this:

1. Go to Develop.

2. Do Settings > Enable Auto Sync.

3. In the filmstrip, select all the photos you want to flip.

4. Do Photo > Flip Horizontal.

5. Do Settings > Enable Auto Sync to turn it off (VERY IMPORTANT).

The Any Shortcut plugin by @johnrellis  will let you assign a keyboard shortcut to this command.