As shown below, any workflow design changes can be pushed to the sleeping process instance(s). 

On the Process Instances page, select the process from the table and click on the Utils - Update - Design menu option.

An Update Design popup window is displayed for confirmation. The application collates all design changes to push to the sleeping process instance (related to the definition). You can click OK to proceed.  

The design changes have been updated successfully with an alert notification, as shown below. 

Note: The values passed to Variables/Globals to a process instance through API are retained by default, regardless of whether the values are correct.