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:When you update the pv name, the new name of the pv will be automatically updated across the process model where the pv is being referenced.

Process model: If you change the name of a process model and Save and Publish it, the new name will be automatically reflected in the Sub-processes,applications which reference it.
This testing was done on Appian 7. Which version are you using ?

I am on 6.7. Hopefully going to 7 soon

Even 6.5.3 I saw it working. process model name change reflects the sub-process node.

One thing to keep in mind is that when you change the name of a process model that new name won't automatically propagate to the Process Display Name (the name the instances of this process get). This can be found by looking at the General Tab of the Process Model Properties. This is one reason that it is a good practice to using dynamic display names.