This setting is only used by the shrink action.

action: shrink
description: >-
  Shrink selected indices on the node with the most available space.
  Reimplement source index aliases on target index after successful shrink.
  shrink_node: DETERMINISTIC
  copy_aliases: True
  - filtertype: ...

The default value of this setting is False. If True, after an index has been successfully shrunk, any aliases associated with the source index will be copied to the target index.