Change initial form field value in views (Django)

I have three form fields that I want to modify/change value of in my views - function one_labeling() before posting the form in the template. The first field is label, where I want to change the initial value in views. Secondly I have two choice fields, pos_tag and head_tags where I use set_head_tags and set_post_tags in views from MultiplechoiceFields post_tags and head_tags in forms in order to post the value of each selected field instead of the number, e.g "NN" instead of 1. At the moment I get the value "NN" for key 1 from pos_tags in forms but I wonder if I could set and modify an initial variable in views for field pos_tags and head_tags as with the field label.

in forms.py

class LabelingForm(forms.ModelForm):

    label = forms.CharField(widget=forms.HiddenInput(), initial="trytrytry22",required=False)

      POS_nodes = (('1','NN'),

          ('2','POSS'),
          ....

        )
pos_tags = forms.MultipleChoiceField(choices=POS_nodes, required=False)



Head_node_choices = (('1','NP'),

          ('2','VP'),
          ...


        )


head_tags = forms.MultipleChoiceField(choices=Head_node_choices,required=False)

 class Meta:
        model = OneLabeling
        fields = ('label', 'sentence' )


    def set_head_tags(self, head_tags):
        data = self.data.copy()
        data['head_tags'] = head_tags
        self.data = data

    def set_pos_tags(self, pos_tags):
        data = self.data.copy()
        data['pos_tags'] = pos_tags
        self.data = data

in views.py

def one_labeling(request, postID):
                form = LabelingForm(request.POST) 
                data1 =  form.cleaned_data['pos_tags']
                data2 =  form.cleaned_data['head_tags']
                if form.is_valid():
                 if data1 and data2:
                    l = data1[0]
                    ll = data2[0]
                    pos_tags = dict(form.fields['pos_tags'].choices)
                    head_tags = dict(form.fields['head_tags'].choices)
                    i = pos_tags.get(l)
                    j = head_tags.get(ll)

                    form.set_head_tags(j)
                    form.set_pos_tags(i)


                    post_one_labeling(request, one_labeling)

For giving initial values for multiple choice fields, you can try doing the following :-

    pos_tags = forms.MultipleChoiceField(choices=POS_nodes,
                     initial=[POS_node[0] for POS_node in POS_nodes])