define

redefines a single configuration property (or a object with properties)

void define(string| object property, [any value] );

property	string\| object	the property name or a object with properties that need redefining
value	any	the new property value (has to be specified when defining the property as a string)

// redefines the width of the datatable
$$("mygrid").define("width", 300);
$$("mygrid").resize();

Details

The component should be refreshed to reflect the changes.

You can use the config property to change the desired configuration option, e.g. a column property:

$$("myGrid").config.columns[0].width = 200;
$$("myGrid").refreshColumns();