Until today a post already on the networks' queue could only have its time moved; any other change meant cancel and redo, losing its log and its first comment. Now the Scheduled tab has Edit: the post opens in the composer with everything it carries (text, media, the per-network copies, the thread, the first comment, the accounts, the time), and Save changes pushes what changed to each network. Each account keeps its own copy, a changed thread on X or Threads is made again, an account added is created and one dropped is removed, and the status line says exactly what each network took. Changes are possible until 6 minutes before the post goes out, which is where the networks stop taking them. The API's update on a scheduled post does the same now, per account.