ATENÇÃO: Um spoiler de Storm of Swords segue ...
Lançado da Patrulha da Noite
Jon Snow teria primeiro que ser liberado da Patrulha da Noite; já que um membro da Patrulha da Noite não pode simplesmente sair, "é conhecido" ...
De acordo com a discussão de Robb e Catelyn Stark quando eles estão indo de Riverrun para o Gêmeos para o casamento de Edmure com a garota de Frey:
[Catelyn]: “If Jon is a brother of the Night’s Watch, sworn to take no wife and hold no lands. Those who take the black serve for life.”
[Robb]:“So do the knights of the Kingsguard. That did not stop the Lannisters from stripping the white cloaks from Ser Barristan Selmy and Ser Boros Blount when they had no more use for them. If I send the Watch a hundred men in Jon’s place, I’ll wager they find some way to release him from his vows.”
-A Song of Ice and Fire: A Storm of Swords, Pt 2 - Blood and Gold (Catelyn).
Um bastardo não pode herdar
Agora vem a questão da legitimidade e herança; Jon não seria capaz de suceder ninguém, independentemente de ser libertado da Patrulha da Noite.
He is set on this. Catelyn knew how stubborn her son could be. “A bastard cannot inherit.”
“Not unless he’s legitimized by a royal decree,” said Robb. “There is more precedent for that than for releasing a Sworn Brother from his oath.”
“Precedent,” she said bitterly. “Yes, Aegon the Fourth legitimized all his bastards on his deathbed. ...
-A Song of Ice and Fire: A Storm of Swords, Pt 2 - Blood and Gold (Catelyn).
Então, Robb pensou muito e sabe que existe é uma maneira de ter Jon Snow liberado do relógio, e depois também legitimado para que Jon possa suceder Robb.
Robb mais tarde escreve um documento; em que acredito que ele decreta que Jon Snow deveria ser legitimado:
Robb stood, and as quick as that, her fate was settled. He picked up a sheet of parchment. “One more matter. Lord Balon has left chaos in his wake, we hope. I would not do the same. Yet I have no son as yet, my brothers Bran and Rickon are dead, and my sister is wed to a Lannister. I’ve thought long and hard about who might follow me. I command you now as my true and loyal lords to fix your seals to this document as witnesses to my decision.”
-A Song of Ice and Fire: A Storm of Swords, Pt 2 - Blood and Gold (Catelyn).
Note que Stannis tenta fazer o mesmo por Jon em Castle Black também.
O Grande Conselho
O Grande Conselho poderia ser convocado para libertar Jon de seus votos e reconhecê-lo como o Herdeiro Aparente. Roubar descaradamente da minha outra resposta :
[Interviewer] Is there any chance that Jon could be released from his oaths of the nightwatch?
[George_RR_Martin] The great council would have released Aemon from his maester's oath, so I suppose it would be possible. With an appropriate authority.
http://web.archive.org/web/20001005212114/eventhorizon.com/sfzine/chats/transcripts/031899.html