Yes, they can be. You may have to experiment on what is the optimal fill-level, but a good place to start is fill it so the filler is
just pooling the liquid on top. But it might take some trial and error to keep it from flooding.
The Npro is a standard RN4081 model, so you can get parts as you need them cheaper from other vendors, most likely. Such as batts, attys and carts. I know you didn't ask, but you may find this useful information! There is a forum for this model here:
RN 4081 *Super Mini* - E-Cigarette Forum
You can get empty carts and fill them yourself, and you can even try different filler materials, like Blue Foam, which is very popular these days. And since you can add your own
juice, you may even want to get into DIY and make your own recipes! That is mega fun!
njoy the Npro!

