Is there a way to change data within a CDT while editing a process instance? I h

If it is just one instance, you can edit the instance and add a flow that enters a new script task that defines the CDT values you want. Then start that flow, making sure it ends without affecting the rest of the expected process model flow.

If it were a large number of instances, you could look into the IFM plugin available under Shared Components

Great. Thanks Steven.