Dragging keywords to another level of hierarchie is similar to renaming, so you get the same warning as you would get, when you rename a keyword.
I found two reasons that a warning might be useful:
- If an image already has keywords, this might be, because you imported images tagged by another application, and you are warned, that the keyword name change might result in inconsistencies with your other source of keywords. So your are asked to reconsider if you really want to do it, just in case you did not know that the keyword is used.
- Renaming might merge keywords, and they are no longer distinctive.
But renaming will (should) not corrupt your Library ...
It would be nice to be able to disable this warning, since it always is extra work to didmiss this warning