Change reference size dynamically (Mapscript)

[Paul james]

Hello, I´m need change reference image size in mapscript (C#)...

I tried that:

mapaObj.reference.height = 100;

but got that error:
Error	8	Property or indexer 'OSGeo.MapServer.referenceMapObj.height'
cannot be assigned to -- it is read only

How can I change that?

Thanks