Hi,
If you don't want that update status to be send why to not check the internal flag on the activity notification itself?
May you want to accomplish what Bruneau is suggesting where the notification not to be send depending on the flag of the activity itself, that will require to create a condition macro with spel code to fetch that information from the alg object.
Not difficult todo but as usual not supported by CA.
That all say. This is good practice to inform your affected end user on the progress of his ticket and this is exactly the purpose of the status field.
If you want to use it for any other purpose I will suggest to create a custom field for it.
Hope this help
/J