I posted some time about my my new favorite pen. One thing that is definitely an improvement over the Rotring 600 and the Rotring Newton is that it allows you easily to change the entire nib unit, and not just the nib. Like Levenger's True Writer line of pens, it mimicks the Esterbrook approach in this regard. What makes this even better is that the L-Tech (and the True Writers) will take any Standard #5 nib. I have recently exchanged the True Writer F nib for a TWSBI Mini Steel Nib Unit - Extra-Fine.
There were two reasons; (1) I like an extra fine nib, (2) the TWSBI Mini nib looks more like the nibs on the original Rotrings and thus better complements the pen. The True Writer nibs have wide shoulders, the TWSBI has almost no shoulders. It is not quite as elegant as the Rotring nib, but it comes close.
The operation is exceedingly simple. Holding the grip section in your right hand, with the nib up grip the nib (and fins) with your left thumb and forefinger. Turn the nib counterclockwise (or the grip and pen clockwise), and it will come out. Screw in the new nib section.