Disabling comments on tasks with specific statuses
This is controlled by a special setting, which is located in the lower part of the additional settings for status sets window:
If you want to allow comments to be added to tasks with the status "New," delete this rule:
You can create any number of rules for adding comments to tasks with a certain status. For each rule, select a Task role and a task status. Users with the given role in tasks with the given status will not be able to add comments:
Each process has its own status set, so you can manage these rules at the process level.