When you draw a shape,maybe,you'll draw some same style shape.you can set the base style of TMyCAD setting before draw it.you can set Brush,Pen,Font properties of tcad first,then when you draw a new shape,it will be effective.

If you draw a line style,you can set ArrowAngle,ArrowLength,ArrowOffset,ArrowStyle properties besides above properties.
Also,you can do it by code.
Code example:

procedure TMainFrm.Button1Click(Sender: TObject); 
begin 
  MyCAD1.Pen.Color:=clGreen; 
  MyCAD1.ArrowStyle:=ADouble; 
  MyCAD1.ArrowOffset:=20; 
  //Draw a line 
  //... 
end;