It's possible if you pretty much gut the whole thing and start over. I don't think the mosfet is the same you would use for parallel. But you have something better than parallel right now. What are you using as an atomizer? What is too much?
Parallel and series use the same type of mosfet. Most commonly a 3034 n-channel mosfet. The other type is a p-channel mosfet. Both work in either type of box, but the wiring is different depending if it's a p-fet or a n-fet.
OP:
In order to change it, you have to be at least comfortable with soldering. If that's no problem, you just change a few wires.. you don't even have to gut the whole thing. I've rewired some tugboat boxes into series.the main thing is to bridge the bottom connections as the negatives and the tops as the positives. Depending on the way it's wired originally, it shouldn't be all that difficult.
It looks like that box uses a n-channel mosfet based on the negative from the top left battery contact running to the mosfet. If you are careful and confident in your soldering ability, all you have to do is disconnect the negative wire from the battery contact, bridge the top two contacts and reconnect the negative wire to the bottom of the battery sled.
I attached a wiring diagram if my explanation was misunderstood.
Also. If you aren't 100% sure you can rewire it, I wouldn't try it. If you mess up it'll auto fire and fry the mosfet.
