keeping old files after upgrade

[mixo <mixo beth uniforum org za>]

Is there a way to make sure that if files have been changed they are 
archived
instead of being replaced? For example, if a configuration file has been 
changed,
make a copy of it, and then replace it (the changed and installed copy) 
with a new
version. More than that, is it possible to include changes made to a 
file in a newer
version of the file when an upgrade occurs? Is it possible detect an 
upgrade?

And another thing, is it possible to generate a file list for an rpm 
instead of
writing out each file name in the spec? I want  to avoid leaving out 
required files
accidentally.