1) Follow the money! I'd expect Bolt to announce approx six months ahead that he's started training to make the 4 x 400 team in Tokyo. For starters that's enough to get media going, the IOC/IAAF a PR b*ner and personal sponsors (old and new) coming to him with open wallets.
2) Expect a maximized media strategy! To keep things exciting but vague he'll then skip the Jamaican trials citing something along the lines of "training's going well but I'm not quite there yet, maybe I'll have to settle for being in the preliminary rounds, I'll bring experience to the team that I'll happily share with the young guys".
3) And if Bolt's running well in the preliminary rounds of the 4 x 400 the Jamaican team will suddenly call a press conference to announce he'll be running in the final too. Bolt only needs one more olympic gold to make it to ten. Risking a loss in an individual event might also risk his legacy (from a then future standpoint) but going after that 10th gold in a realy has no real possible downsides.