Yes. It may not become their "best" role.... but as I said in another thread today, the role & duty circles aren't absolutes. They are how the game interprets their skills. If you train up a the prospect for several years as a Ball Playing Defender, they shoudl become a very proficient defender on the ball. Even if their little circle still says "Defensive Centre Back".
Another factor is that certain highly specialized roles have CA minimums, and a brand new regen is unlikely to hit that minimum. I know Complete Forward does. Wouldn't be surprised if Complete Wingback does as well.
Be reasonable with your expectations, though. If your 5-star 16 year old fullback has 2 in Crossing, Dribbling, Passing, Technique, Vision, and Off the Ball.... don't expect those all to be 15+ once he's fully develop. Some just won't be. That said, almost no attributes function in isolation, so even one or two being mediocre won't mean they can't play a role. I've had consistent killer attacking performances out of fullbacks with Crossing of below 10, because other attributes can compensate to a degree. Conversely, great Crossing won't mean as much if they won't have Technique, Decisions, Anticipation, and the physical ability to create space, etc.