$HOSTTYPE and related topics.

[Matt]

Hi folks

Just a couple trivial queries here. I have an AMD Athlon Thunderbird CPU
and my $HOSTTYPE is currently "i386". I thought it would have been
either "i686" or maybe even "athlon"? I realise the machine architecture
is an i386 compatible but I thought the exact architecture would have
been more appropriate. `arch` correctly reports "i686". 
Related is the $MACHTYPE. It's set to "i386-redhat-linux-gnu". Again,
should this not contain i686? Also, are there plans to change this to
fedora? i.e. "i686-fedora-linux-gnu". 
Lastly, is it safe to change these values myself? Or do certain apps
rely on them being the values originally set? 

TIA
-- 
Matt