Change the widget of just one field in django-crispy-forms with the layout object AppendedText

I am using django-crispy-forms to render the form of a model in django. django-crispy-forms already integrates very well with Twitter Bootstrap and has defined a layout object for the `AppendedText` widget: I have the following model in my django `models.py` ``` class Historia(models.Model): persona = models.ForeignKey('Persona', blank=False, null=True, related_name='historias') fecha = models.DateTimeField(unique=True, auto_now_add=True) motivo = models.TextField() peso = models.DecimalField(blank=True, max_digits=5, decimal_places=2) talla = models.IntegerField(blank=True) tension = models.CharField(max_length=15) pulso = models.IntegerField() diagnostico = models.TextField() tratamiento = models.TextField() pendiente = models.TextField(blank=True) ``` and I define the following `modelform` in `forms.py`: ``` class HistoriaForm(django.forms.ModelForm): class Meta: model = models.Historia def __init__(self, *args, **kwargs): super(HistoriaForm, self).__init__(*args, **kwargs) self.helper = FormHelper(self) self.helper.form_class = 'form-horizontal' self.helper.form_tag = True self.helper.form_id = 'nueva_historia_form' self.helper.form_action = 'nueva_historia' self.helper.form_show_errors = True self.helper.error_text_inline = False self.helper.add_input(Submit('crear', 'Crear')) ``` My question is how can I change the widget of the `peso` field without having to create a new `widget` subclass since `django-crispy-forms` already defines a layout object. Please also note that I do not want to enumerate all other fields in order to do this like: ``` self.helper.layout = Layout( Fieldset( 'Legend', 'nombre', 'apellido', AppendedText('peso', 'kg') ), ButtonHolder( Submit('submit', 'Submit', css_class='button white') ) ) ``` since I will have to keep editing the helper layout if I decide to add new fields in my model from which standard widgets are already very useful. Edit: I have also seen the methods to access the layouts in a helper like `self.helper.layout[0] = AppendedText('peso', 'kg')` but I do not know the index of the field I would like to change and it would be much nicer if I could just write `self.helper.layout['peso'] = AppendedText('peso', 'kg')`