You cannot change everything in processes that are part of a product system, e.g. not remove flows that are connecting to other processes, but anything you can change is reflected once you save the process and reload the product system, also parameters. You will need to add newly added process parameters to the product system or project, since product systems and projects do not use automatically all parameters of the processes that are part of the product system, but only a user-defined subset. I would not see a way how the user-selection of new parameters could be skipped (if this was your question)? If not all process parameters are automatically entered in a product system of course?