是的，AWS ECS任务定义YAML配置可以扩展。一种方法是通过使用AWS CloudFormation模板来扩展YAML配置。以下是一个例子，展示如何扩展AWS ECS任务定义YAML配置：

Resources:
  TaskDefinition:
    Type: AWS::ECS::TaskDefinition
    Properties:
      Family: my-task-def
      ContainerDefinitions:
        - Name: my-app-container
          Image: my-image
          Environment:
            - Name: FOO
              Value: bar
          Command:
            - python
            - app.py
          Memory: 512
      Volumes:
        - Name: my-app-data
          Host:
            SourcePath: /mnt/data
      NetworkMode: bridge
      ExecutionRoleArn: ecsTaskExecutionRole

  MyTaskDefinition:
    Type: AWS::ECS::TaskDefinition
    Properties:
      Family: my-task-def-extended
      ContainerDefinitions:
        - Name: my-app-container
          Image: my-image-extended
          Environment:
            - Name: FOO
              Value: baz
            - Name: BAR
              Value: qux
          Command:
            - python
            - app-extended.py
          Memory: 1024
          VolumesFrom:
            - SourceContainer: my-data-container
              ReadOnly: true
        - Name: my-data-container
          Image: busybox
          Volumes:
            - Name: my-app-data
              Host:
                SourcePath: /mnt/data
          Command:
            - sh
            - -c
            - "while true; do echo \'Data container running...\' ; sleep 10 ; done"
      Volumes:
        - Name: my-app-data
          Host:
            SourcePath: /mnt/data
      NetworkMode: bridge
      ExecutionRoleArn: ecsTaskExecutionRole

在这个示例中，我们定义了两个AWS ECS任务定义，其中第二个任务定义“MyTaskDefinition”是对第一个任务定义“TaskDefinition”的扩展。 MyTaskDefinition将映像"My-image-extended"用于容器“my-app-container”，并添加了新的环境变量“BAR”