Allow User to Change Slots
Create an iron python script for the game's Custom Icon event with these lines. Check "Prompt for variable values" and allow user access.
ThisService.Slots = int(ThisService.Variables["CustomSlots"]); ThisService.Save(); ThisService.Configure();
Create a new variable named "CustomSlots". In the variable settings tab check "Script parameter" and "Save script parameter value". Allow user access. Set the type to NumericTextBox.
With that your user should be able to see the icon in the service home page to change the slots.