How to change the existing form element type and it's order in form when using modelForm

class MyForm(forms.ModelForm):
    OPTIONS = (
        ("IN", "India"),
        ("US", "United States"),
          )
    countries = forms.MultipleChoiceField(widget=forms.CheckboxSelectMultiple, label = "Select Medications", choices=OPTIONS)
#To change the order use the below code
    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.fields.keyOrder = ['name', 'countries', 'states']

    class Meta:
            model = MyModel