[Chimera-users] Edition of the pdb/trajectories via Chimera

Dear Chimera Users! I have a pdb file for the 16 monomers of the coarse-grained GPCRs and its corresponded trajectory in dcd. In both files all the monomers are defined as the same letter of the chain (X). My question: are there an easy way to assign a unique letter to each of the monomers in the both files via Chimera to facilitate the further analysis ? Thanks so much! James