I don’t add milk to my Huel, but have tried rice milk and Huel. It’s quite thin, compared to other milks and definitely sweet. But if you have rice milk perhaps you like the sweetness? In terms of nutrition, from what I understand rice milk is high in carbs, but relatively low in protein and fats. If it works for you then great! But for me, reducing down that nutritious Huel BE for rice milk might not be ideal since it’s not adding so much more.
I don’t usually have rice milk but I was just seeing if I could get the carbs up and reduce the protein down a little down to something that may suit me as I’m not athletic nor a body builder. 63g of black is still 28g, so no small amount.