which local.cf/user_prefs.cf?

[Jerry Malcolm]

I have read that I should add customization to local.cf.  But on AWS 
Linux I have a local.cf in /usr/share/spamassassin.  It says this is the 
place to make changes.  But there's another local.cf in 
/etc/mail/spamassassin that looks like it has some customization in it 
as well.  It says the values are overwritten by editing 
~/.spamassassin/user_prefs.cf.   I added some score changes to the 
/usr/share version, but the scores don't appear to be affected.  That 
may be a different problem. But I'd prefer not just blasting every 
possible config file with the same data hoping I hit the right one.  So 
could someone clarify the different uses of each of the files (including 
user_prefs.cf) and let me know the guidelines for when to use which one?

Thx