Design variables are a great way of organizing your most important or most often used parameters into a single location for easy access and manipulation. You may also save the design variables to a text file that can be loaded at any time to update your model. These text files can be edited outside of OpenVSP either manually or by scripting/automation and then used to rapidly update models with parametric variations on design trades. This is a nice way of handling trade studies and systems analysis without having to build the API or write in AngelScript.
Design Variable Introduction
Adding, Removing, and Adjusting Design Variables
Saving or Loading a Design Variable File
Modifying and Executing a Design Variable File
Finding Parameters Using the Design Variable Explorer
Design Variable Conflicts and How to Avoid Them