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You need to create a rule input that stores whether you're creating or updating. You'll define that value in your process / processes before you load it into the form. You use showWhen parameters throughout your form, as well as disabled parameters throughout your form to control how all the components behave, and you wrap two sets of save functionality on your Submit button with an if(). If isCreate is true, do the create set of save functionality, otherwise do the edit set of save functionality.