The following snippet will be helpful in setting up the mode of the query criteria in programmatic way.

public Boolean setAdvancedMode(){
              QueryDescriptor descriptor =
                      (QueryDescriptor)evaluateEL
                  ("#{bindings.SearchCriteriaQuery.queryDescriptor}");
              descriptor.changeMode(QueryDescriptor.QueryMode.ADVANCED);
             return true;
}

public Object evaluateEL(String el) {
        FacesContext facesContext = FacesContext.getCurrentInstance();
        ELContext elContext = facesContext.getELContext();
        ExpressionFactory expressionFactory =
            facesContext.getApplication().getExpressionFactory();
        ValueExpression exp =
            expressionFactory.createValueExpression(elContext, el,
                                                    Object.class);
       return exp.getValue(elContext);
    }