Updating rather than replacing ECS Task Definition with CloudFormation
Yes, in order to put your changes in a new revision of the same Task Definition you should use the Family parameter. Quoting from the official documentation:
Family
The name of a family that this task definition is registered to. A family groups multiple versions of a task definition.
CloudFormation will still consider this a "replacement" and will delete the old revision, however it will not create a new Task Definition if you use the Family parameter.