This study clarifies the effect of the nature of solid N-precursor molecules on the N-modification, more specifically unravels how solid N-precursors – here cyanamide and melamine - affect the physicochemical and catalytic properties of the resulting carbonsupports and final catalysts. Using such modified high surface area carbons, in situ measurements as humidity dependent performance, electrochemical surface area, proton resistivity and limiting current measurements were conducted to access the role and degree of ionomer coverage and transport resistances. Additional X-ray photoelectron spectroscopy (XPS) proves molecular interaction between acidic side chains and basic N-groups. Overall, we show the importance of the N-precursor and synthetic route determining which physicochemical parameter will be influenced in the resulting catalytic layer. Based on this, the pure presence of some N-moieties does not guarantee an improved ionomer distribution, but the modification process enables a tailoring effect of the carbon species itself affecting transport phenomena.