AutoCAD .NET :: How To Set Variable In C#

Im Currently working on c# automation.Since im using autocad interop im not able to understand the process of setting

variable in autocad..I have drawing files with different dimension styles used inside..I can filter the dimension by selection set . But the problem is im filtering through dimstyle name.Is there any dxf code for selecting all kind of dimension styles.So that it will be useful for me.

But my problem is i need to apply one particular standard dimstyle to all my drawings. How i could set variable to my new dimstyle(new). This is my code for setting variable ,but its not updating in my current document.

this is my code;

double a = Convert.ToDouble((acadDocument.GetVariable("DIMASZ")));
object b = Convert.ToDouble(2.5);
acadDocument.SetVariable(
"DIMASZ", b);