Tomallyn,
If I am not mistaken, Chartpak will exchange your nib to one of your preferred size within one month of purchase. This is a no cost service for Pelikans, and the turnaround is about 10 days.
It is OK if your pen was previously inked, so try out the nib first. There are variations from nib to nib, so the nib supplied may be perfect for you.
Here is link....
http://www.chartpak.com/Good luck and enjoy!
Mike