how can I change the modelform label and give it a custom name
From the documentation:
You can specify the labels, help_texts and error_messages attributes of the inner Meta class if you want to further customize a field.
There are examples just below that section of the docs. So, you can do:
class Meta: model = Post labels = { "video": "Embed" }
An easy way to achieve this without editing the form would be to change the verbose_name on the model. For the video field on your model you could change the label on the form from "video" to "embed" like so:
class Post(models.Model) video = models.UrlField(verbose_name="embed") # Other fields