Being overfull will cause its own problems, but it shouldn't have any effect on how the clutches themseves perform. If it's way over the top now then it may well have been low when you had the problem, and raising the level has cured that, but you've just gone a bit OTT. Overfilling it could cause it to eject fluid out of the breather, and cause leaks from places that are under the fluid level that shouldn't be, but if it's not ejecting fluid, and it's not massively overfilled, then I'd be inclined to use it and see what happens. If the clutches fail then there won't have been anything else you could have done to prevent that happening.