Users can create as many change tasks as required within a change notice. You can also create soft types of change activity, each implementing different attributes, life cycles, workflow, team, permission etc if you need to.
Take care with these kind of changes though as change object workflows reference lifecycle states of other change objects. (not just the primary business object)
The change notice workflow then listens for state COMPLETED or CANCELLED on all the related change activities before delivering the change audit work item. This means all the change tasks have to be resolved before the change notice can complete.
In 10.1 it is possible to sequence the delivery of change tasks, if you have ProjectLink installed.