This is part of managed list plugin system.
List plugins can have entries removed from them by using the list_remove plugin.
Move items from account to another.
trakt_list:
username: <USER A>
list: watchlist
type: movies
accept_all: yes
list_remove:
- trakt_list:
username: <USER B>
account: traktusername # required if list is not public
list: watchlist
type: movies
Uses: trakt_list, accept_all