Various candidate processes that can effect rearrangement of the shell of addends are being discussed for C60Fx and C-60(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 C-60 in distribution of products of their high-temperature syntheses.