Playing as an octoling was as simple as changing a "playertype" variable to 3 instead of 1 or 2. 1 and 2 are the female/male Inklings. That being said, if playable Octolings are going to be a thing, we'll definitely need a patch. While the Octolings are playable by yourself and visible to other players, if you get an Octoling in your plaza, it apparently softlocks the game.