Tasks can be reprioritized, or have client_batch_id changed in bulk by a request to the API. You need to supply the array of task ids, and the new values.
Tasks with lower priority values will be worked on first, and the default is 0. Range of value is between -2147483648 and 2147483647.
The client_batch_id field is a string specifying the task’s new client_batch_id.
Please inform your project manager if you update a task's client_batch_id, as it can affect reporting.
There is no hard limit on the number of tasks that can be submitted for a bulk priority update, but there is a chance that requests with a large number of tasks fail with a 5xx error. A safe limit to avoid such errors is 100,000 tasks.
You can check current task info via the Get status of a set of tasks endpoint.