[PyMOL] mutagenesis

[Eric Z. <zo...@ca...>]

All-
    I have been attempting to add atoms to proteins that are missing 
electron density, mostly surface positions.  In most cases I have been 
able to just add an atom or two (Build->Fragment->group); sometimes 
adding a whole rotamer is required.  I have been unable to add a planar 
guanidino group or the planar oxygens to Asp or Glu.  How would I change 
hybridization of atoms to get the correct geometry?
Also, where are the rotamers in pymol from?  Are they backbone dependent 
or independent?  How hard would it be to use a different set of rotamers?
Thanks.
Eric