You've got roughly 20ish, and they're just kinda wandering around the continent eating whatever comes their way. None of them have wandered into the ork/ayacmanik battleground.
It's definitely possible to modify god portfolios, yeah, though outright additions will probably be a case-by-case basis.
The afterlife thing, however, will definitely come about - once a death god comes about and creates a relatively 'neutral' afterlife, it allows for other gods in the same pantheon to have personalized variants for their believers. To give an Old World example, everyone goes to Morr's garden at first, but depending on their beliefs they might stay there, go to Sigmar's vaguely Valhalla-ish halls, head to Verena's libraries, wander to Shallaya's paradise, etc, depending on what god they followed most strongly.