After some more tests, I found the real trigger is the tab key. You can always trigger the update whenever you want(e.g. after deleting an item): directly pressing the tab key to trigger the re-numbering of the current item and the items below which are with the same indent level:

NOTE: The items above the insertion are not affected.
NOTE: The child items are not affected.
btw, you may need to delete the inserted tab key after the update.