Conditionally show and hide a form field and set the field value

I have a form in my Django that looks something like this:

class PersonnelForm(forms.Form):
    """
    Form for creating a new personnel.
    """
    username = forms.RegexField(
        required=True, max_length=30, label=_("Name")
    )
    is_manager = forms.BooleanField(
        required=True, label=_("Is Manager")
    )

I use this form in two places in my site. One one of the places, I'd like to display the form and all of its fields except the is_manager field but I would like to set the default value of this field to True. In the other place, I'd like to display the form and all of its fields including the is_manager field and I would like it to have a default value of False.

How can I accomplish this? Seems to be a trivial thing but I can't figure it out.

Thanks.