I could be wrong (there might be something new on the market), but once those 2 part urethanes set up, they're solid. I can't imaging a magic goo that would soften them without also softening the substrate (also a 2 part resin).
I've had some spots on my boat where two part urethane (Interlux) has lifted, mostly on inside radii between the deck and the house where my prep might have been a bit light. I'm afraid that you're going to have to take down the non-skid and then restore it. I think I'd try a wire brush first - might get you where you want to go.