But when I add another macro that uses Button 5 + Shift, it brings up a conflict menu. I don't want this to happen, I want to be able to press the button alone to trigger one thing and with shift to trigger something else. Am I doing something wrong here?
Try this: in the first of your macros (the F12 one) change the trigger "ignoring modifiers" to "with these modifiers" but without selecting any modifier keys like this:
Both macros now look to see if any modifiers are used.