I have attached a macro which shows two ways how you can modify the distance value for reference plane. You should select the reference plane in the feature tree and specify the value for NEW_DISTANCE constant. There functions shows two different ways of doing this modifications:
ChangeDistance1 - change through the feature data
ChangeDistance2 - change the driving dimension
You can easily modify the code for C#. Let me know if you have any problems with this.
Application Engineer at Intercad
Tel: +61 2 9454 4444
Thank you Mr. Artem