Yes, but when someone rolls to, say, attack, by the time they've posted they've already rolled. I could say "The next time so and so attacks they use my portent roll instead" but that still limits my ability compared to how it would normally work in a tabletop game (the advantage being that, since it's in realtime I can immediately react to a changing situtation). Especially in how enemy attacks work, I have to commit to replacing an enemies roll before they even decide what they're doing (since you'll roll their attacks as soon as you post). If that's how it's going to work that's fine, it's not something I'm going to fight over, I choose diviner because of the backstory I had come up with (I came up with the idea first and then said "It makes the most sense for her to be a diviner") But it does mean I have an ability that really doesn't work how it's supposed to anymore.