task_change: Change a task in a TaskList
In henfiber/later: A Periodic Batch Processing Framework

Change the definition of a Task and return the updated TaskList

1	task_change(task_id, TaskList, schedule, FUN, args, method)

`task_id`	The id of the task you want to change
`TaskList`	An existing TaskList list
`schedule`	A shorthand period to recurrently run this task
`FUN`	The function to run
`args`	Optional arguments to FUN
`method`	Whether to run in the parent process or in a parallel R process