Custom Keyboard Shortcut to switch tabs in Photoshop on Mac

This answer is not Photoshop-specific, but might work anyway, if it's a reasonably well-behaved OS X application.

If there are menu items for these commands (like Select Next Tab in Safari's Window menu), you can assign them different keyboard shortcuts in System Preferences » Keyboard » Keyboard Shortcuts » Application Shortcuts

Select the application (e.g. Safari), enter the menu item title (e.g. Select Next Tab) and enter the desired keyboard shortcut (e.g. Cmd-Shift-[).

Result:

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The same preference pane contains the OS X global shortcut for cycling through an application's windows:

Change this setting to change it for all applications.

Press Command (Control on Windows) and the ~ (the tilde key) Here is a link to more info: http://vectips.com/tips-and-tricks/quick-tip-quickly-switch-between-open-tabbed-documents/