For doing 2.0.2 to 2.1, you are on a stable branch and not that much
has changed in terms of interfaces.   I am 99.9% sure you don't need
to update bootblocks.

I'd

a) get all the release sets on the machine

b) unpack and install the new kernel

c) reboot

d) unpack and install all the sets except etc.tgz and xetc.tgz

e) merge the etc changes somehow

f) reboot

A further tricky bit is that the ipf user/kernel interface changes
sometimes, and the old ipf tools won't work with the new kernel.  So
if you have IPFILTER_DEFAULT_BLOCK, you'll be stuck.

So, I recommend that you get a spare local box, install 2.0.2,
configure ipf the same way, and  do the upgrade 'remotely' when you
could touch if you had to (but don't), making careful notes.  Then try
it for real, and please post your experience.

-- 
        Greg Troxel <gdt@ir.bbn.com>