How to programmatically set custom field data in the form for creating a new Prefix

[sstojanovic-godaddy]

Netbox v4.2.3

Working on a plugin to dynamically pre-populate some fields in the Prefix form based on the parent object.

I implemented a custom alter_object method on the PrefixEditView.

The issue is that custom field data that I set this way is not displayed on the form. Other fields (Site, VLAN etc...) work just fine.

My code (simplified):

def custom_alter_object(self, obj, request, url_args, url_kwargs):
    # Find parent
    prefix_param = request.GET.get('prefix')
    parent_prefix = find_parent_prefix(prefix_param)

    # Get parent data
    parent_cf_value = parent_prefix.custom_field_data['my_cf']
    parent_vlan_id = parent_prefix.vlan.pk

    # Set values on new prefix
    obj.vlan_id = parent_vlan_id      # this gets rendered in the UI on prefix form
    obj.custom_field_data = {'my_cf': parent_cf_value}     # this doesn't get rendered in UI

    return obj

setattr(PrefixEditView, 'alter_object', custom_alter_object)

Is there another (better) way to achieve this or am I doing something wrong?