It would be very useful to assign "CTRL + PGUP" and "CTRL + PGDN" to "Previous Tab" and "Next Tab," because this is the same hotkey used to switch tabs in web browsers, like Firefox. Unfortunately, there is a mysterious force preventing this assignment from taking hold. The keyboard customization window returns gives no error when assigning these keystrokes to the custom commands (MC.SetActiveTab PANEL=ACTIVE TAB=NEXT, MC.SetActiveTab PANEL=ACTIVE TAB=PREV). The custom command works perfectly when assigned to Left / Right and other hotkeys. When keying in the keystroke, "CTRL+PGUP," the entry field instead reports "CTRL + NUM 9" - fair enough, I guess, that's also used to switch tabs in browsers - but the column in the upper window reports the keystroke only as "CTRL +", and neither Ctrl+PGUP nor Ctrl+Num9 trigger the command. Upon exiting and re-entering the keyboard customization window, and clicking on the command in the list, it is still reported as "CTRL+NUM 9" in the lower entry field, and still reported as only "Ctrl +" in the upper column display. I have banged my head against the wall repeatedly to no avail.
Considering this is the default keyboard shortcut for navigating tabs within browsers, it would be nice for this to work. I have mapped gamepads that are used interchangeably for both web browsing and in other tabbed file-navigation tools. Hopefully this can be fixed (unless I'm an idiot and have missed something obvious).