Various candidate processes that can effect rearrangement of the shell of addends are being discussed for C₆₀F_x and C₆₀(CF₃)_y compounds. It is shown that isomerization of fluorofullerenes is catalyzed by other fullerene molecules or organic donors, while in trifluoromethylated fullerenes such catalysis is inefficient. These observations afford an explanation for important differences between fluorides and CF₃ derivatives of C₆₀ in distribution of products of their high-temperature syntheses.