Someone else reported trying to take one apart on one of these 599 item/topics, and found the "hood" to be glued to the section, and so not removable, and you can't get the nib/feed out without removing the hood.
I can confirm that the nib on the hooded varieties will simply pull out, leaving the feed in place. Then you can work on the nib, or whatever you're doing to it, and then just push the nib back in over the feed and line it up properly and you're back in business.
I bought a dozen of the Jinhao 599 clear plastic "medium" standard nib variety, and a dozen of the 599 clear plastic hooded fine nib variety. Nearly every pen wrote very nicely straight out of the box, on both varieties. Only a few needed any nib smoothing and that was it; no DOA pens! I pulled the nib out of one of the hooded fine nib pens just to play with tuning it a bit, and it pushed back in and it writes nicely with no problems.
One thing I notice with the hooded variety is that the feed is longer than it is on the standard nib version. The end of the feed extends into the converter slightly, so the piston on the converter cannot be extended all the way down without hitting the end of the feed. So, if you keep twisting the converter after it makes contact with the feed, it will dislodge itself; with the potential of damaging the end of the piston if you repeatedly do this. It's best just to not extend the piston all the way!
These pens are attractive and write so well that it's hard to knock them at all, for what they are. And, as mentioned already, they make great beginner pens for friends who want to give fountain pens a try.
It's too bad the barrels have the Safariesque slotted windows in them, otherwise these might make pretty good eyedroppers!