On Swapping Pelikan Nibs
As a rule, I caution people about casually swapping nibs into and out of vintage Pelikans. While the pens have interchangeable nibs, the purpose of exchanging nibs on a Pelikan was, and is to allow retailers to offer customers a wide range of nibs without carrying a huge inventory. Today that need is obviated by the relatively few nib grades available, but Germans do not readily change successful design features (see the Porsche 911and BMW's straight six engine).
While vintage Pelikans from the 1950s through the 1970s are plenty robust, over time the acrylic plastic of the sections, which are integral to the barrel, lose some elasticity and there is a chance of cracking the section or damaging the feed or alignment while changing nibs.
Although it seems self-serving on my part, I strongly suggest simply buying another pen. The low cost 120s, 140s, M200 pens are perfect for this purpose.