The unexpected isomerization of N-ethyl [6,6]-pyrrolidino-Y3N@C-80 to the [5,6] regioisomer is reported, as well as the synthesis, characterization, and electrochemical analysis of Er3N@C-80 derivatives. A complete electrochemical study of the M3N@C-80 species (M = Sc, Y, Er) and their derivatives is presented. We introduce electrochemistry as a new tool in the characterization of the [5,6] and [6,6] regioisomers of trimetallic nitride endohedral metallofullerenes.