Dear Dr. Ferrin,
Hope this email finds you the best of your health. First of all, I did appreciate the effort that You and Your team did in the form of UCSF Chimera. Being the part of academic/government university, I have used Chimera tool for protein modeling and cited in my two articles: one published in JCB-Wiley and other in Hundawi in 2014. Current email I am sending to request for guidance about how can I substitute an amino acid (wild type to mutant residue) within protein 3D model by using Chimera. I will be thankful for your guidance, if possible.
With regards
 
Hussain MR
PACER-HD, KAU, KSA