A simple group-theoretical approach, which is based on the subgroup decomposition of the isomer permutation representation, is applied to enumerate the substitution isomers of three fullerene cages, D-2-C-76, D-2-C-84, and D-2d-C-84. Several rules governing the symmetry distribution of substitution isomers are extracted from the enumeration results. These rules are also applicable to other substitution frameworks.