What would happen if I were to run the same Process ID twice consecutively without adding any transactions?

If you were to unintentionally run the same process ID a second time without having added transaction(s), no unintended consequences will occur. One way to see how this works is to run a Mekorma Action Board Process ID to completion, and without generating anymore transactions when you run the same process ID  you will notice the process run a second time but on the second run the report at the end will show zero dollars were processed.