I have a cloudformation template for creating a security group as follows. It references tags.yaml that contains pre-defined tags in a s3 bucket.

Resources:
  EC2SecurityGroup:
    Type: "AWS::EC2::SecurityGroup"
    DeletionPolicy: Delete
    Properties:
      GroupDescription: Test Security Group.
      GroupName: !Ref SecurityGroupName
      SecurityGroupEgress:
        - Description: Direct traffic to all destinations.
          CidrIp: "0.0.0.0/0"
          IpProtocol: -1
      SecurityGroupIngress:
        - Description: Sec. group of LB.
          FromPort: 80
          IpProtocol: tcp
          SourceSecurityGroupId: sg-xxxxxxxx
          ToPort: 80
      VpcId: !Ref VPCId
      "Fn::Transform":
        Name: AWS::Include
        Parameters:
          Location: "s3://{bucket-name}/tags.yaml"

I want to now append/add additional tags in this template. Is that possible? I tried adding Tags property but that didnt work. Example:

      "Fn::Transform":
        Name: AWS::Include
        Parameters:
          Location: "s3://{bucket-name}/tags.yaml"
      Tags:
        - Key: TestName
          Value: DummyVal