Changing the shortcut for highlighting text in Preview
In OS X El Capitan 10.11.4 - macOS Catalina (10.15), you are able to set up a custom shortcut like this:


Open the Preview app.
Enter Preview -> Services -> Services Preferences


Choose App Shortcuts


Click on the + button and the fill in the fields like below. It is important that the Menu Title perfectly matches the operation name to which you want to assign the shortcut.


Done. Now you can highlight text in Preview using your custom shortcut.