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You can switch the numbering to the left of the task names into outline form. Choose "Use Hierarchical Numbering" from the View menu.

You can also add any kind of custom data to tasks that you want, but then of course you'll have to enter all the data manually yourself.

If neither of those is what you're looking for, could you try and explain a little more? If a task's unique ID is based on the hierarchy of tasks, then what happens if a task is moved to a different task group? Should it get renumbered or keep its original number?