Remove 'Delete selected model' button from related model fields in model creation form (Django admin)

In my models I have Document model with foreign key to the Library model. When I am in Django admin site I want to disable editing and deleting Library instances when I am creating new Document.

What I tried was to remove delete and edit permissions by subclassing django.contrib.admin.ModelAdmin and removing change/delete permissions

@admin.register(Library)
class LibraryAdmin(admin.ModelAdmin):
    def has_delete_permission(self, request, obj=None):
        return False

    def has_change_permission(self, request, obj=None):
        return False

This makes unwanted buttons disappear but also entirely blocks possibility of editing and removing Libraries, which is not what I want. Is there a way to disable these actions only in model edit form?

You could mark the request in the document admin:

def changeform_view(self, request, object_id=None, form_url='', extra_context=None):
    request._editing_document = object_id is not None  # add attribute
    return super(DocumentAdmin, self).changeform_view(request, object_id=object_id, form_url=form_url, extra_context=extra_context)

Now you can access that flag in the related admin:

@admin.register(Library)
class LibraryAdmin(admin.ModelAdmin):
    def has_delete_permission(self, request, obj=None):
        if getattr(request, '_editing_document', False):  # query attribute
            return False
        return super(LibraryAdmin, self).has_delete_permission(request, obj=obj)