That depends on your current code. If you are disabling the shutter button in software when there is not enough credit, then probably the easiest solution is to have “free mode” button that toggles a flip-flop. If the current code returns false when shutter should be disabled, the free-mode flip-flop output should be or’d with that to determine if shutter should really be disabled (i.e. shutter will be enabled if there is credit or free-mode is enabled). You will need additional code to change LCD to display “free” instead of credit (an if-else node could be used for that…Cond would be state of free-mode toggle; T & F would be credit or “free” with output fed to LCD)
If you want multiple modes, you could have multiple toggles, or base mode on a number and store mode # in a single count node. Count would probably be easier to code if you have a single mode button. Multiple toggles might be easier if you have a separate button for each mode.