Yeah, you can do that if you want. I am guessing the multipool using an exchange like bittrex behind the scenes to convert your mined coins into HYPER. I'm not sure if doing the exchange manually is "easier (although more time consuming)". After all, you are proposing the manual exchange method to speed up the conversion in the first place. I would describe it as opposite. It's probably not as easy but less time consuming than waiting for the multipool to auto-convert. I haven't used the multipool, but it seems from what you are saying that the multipool takes a long time to convert your mined coins to HYPER.

Anyway, yes, you have the option to manually convert your coins into HYPER. I think it also gives you a little more power and flexibility to choose when and how much to convert to get the best bang from the market.