Enable users to occupy multiple identities in the same thread

[essential-randomness]

Allow users to choose another identity after already being assigned an identity in a thread (either random, or via role).

Use cases

• Moderation without identity reveal
• Roleplaying multiple characters
• Filling your own prompt on e.g. a kinkmeme

Possible vectors of attack

Everything related to sock puppeting. Some examples:

• Faking broad consensus over an issue
• Artificially escalating situations by "roleplaying" both sides of a conflict

Open questions

• Who should be able to see that more than one identity is being used in a thread? Under which preconditions?
• Who should be able to see which posts come from the same identity in a thread? Under which preconditions?
• Should this ability be governed by a permission? At which level should the permission be set?
• If the ability to see matching original identity can be "triggered", who should be notified about it triggering?

Related threads

• https://v0.boba.social/!bobaland/thread/c00d8638-9a7a-478e-8230-22bbe38da031