What is the Appian refactoring ability? If I rename a pv will all teh code

Process variable name changes get updated in your process models, except when they're listed explicitly in rules or expressions. Those references must be updated manually. However, the process model validation should catch these and throw an error -- which links to the activity where the old name is being used.
As far as changing the display name of a process, it doesn't change existing instances (running, completed, or archived). Only new process instances started from the model will take the new process instance name.

Process variable name changes get updated in your process models, except when they're listed explicitly in rules or expressions. Those references must be updated manually. However, the process model validation should catch these and throw an error -- which links to the activity where the old name is being used.
As far as changing the display name of a process, it doesn't change existing instances (running, completed, or archived). Only new process instances started from the model will take the new process instance name.