code: def copy_and_move_messages(from_channel, to_channel):
          
          with BlockSave(Message, query_dict={'channel_id': to_channel.key}):
              for message in Message.objects.filter(channel=from_channel, typ=15):
                  message.key = ''
                  message.channel = to_channel
                  message.save()
docs: While splitting channel and moving chosen subscribers to new channel,
           old channel's messages are copied and moved to new channel.
  
           Args:
              from_channel (Channel object): move messages from channel
              to_channel (Channel object): move messages to channel