Template Customizing
The calendar is not yet available for customizing, but the input field template can be customized. First you have to create a HTML template for widget input.
<!-- File: my_app/templates/my_app/custom-input.html -->
<h5>This is a customized input from template</h5>
<div class="input-group dbdp">
{% include 'django/forms/widgets/text.html' %}
<div class="input-group-addon input-group-append input-group-text">
<i class="{{ addon_icon_class }}"></i>
</div>
</div>
Then add it to BOOTSTRAP_DATEPICKER_PLUS settings.
BOOTSTRAP_DATEPICKER_PLUS = {
"template_name": "my_app/custom-input.html",
}