To set the default setting for an object, you first need to know the ancestor of the object whose property you wish to set. To find the parent of an object, type the following:
h=get(object's_handle,'Parent')
To set the default, type the following:
set(h,'DefaultObjectPropertyName','PropertyValue')
Don't put any spaces in the DefaultObjectPropertyName expression. A good example of how to do this is the following:
set(gca,'DefaultLineLineWidth',10)
Any line you plot after this statement will have a line width of 10.