When translating "return", you must often choose between "rentabilité" and "rendement". For a fund, I would use "rentabilité". Given the context, I would not translate "load" as it would be too repetitive in this sentence (or definition). I would simply say "La rentabilité ajustée s'entend après impact des frais de cession." But if you want to be precise, you can say "rentabilité après frais de cession" or "rentabilité ajustée/retraitée des frais de cession".