[BioPython] Homology Modeling question

[Omid Khalouei]

Hello,

My question is not specifically related to Biopython, I wanted to know if 
homology modeling can be used reliably to see the effects of single amino 
acid substitutions. I mean is homoloy modeling useful for predicting the 
structure of those sequences for which there is no know structure or can it 
also be used for a more "fine tuning" analysis such as changing one amino 
acid on a PDB structure and then performing homology modeling using that 
same PDB structure as template?
Also is there any uptodate forum for homology modeling? I looked it up on 
Google but postings were for back in 1990's.

Thanks for your help.
Omid K.