[PyMOL] Mutagenesis

Could anyone tell me how to replace amino acid residues in Pymol. 
Specifically, I want to replace Proline 30 and Isoleucine 32 with 
cysteines in horse cytochrome c (PDB: 2FRC).  Can I do energy 
minimization? I am using MAC OSX version.

Also, is there any way to position a ligand such as Ca ion or Mg ion?

Thanks

Xiang