safest way to 12.1 -> 12.2

I just burned a DVD to upgrade my 12.1 -> 12.2 on my production machine. I have lots of utilities installed and so cannot format and fresh install. The locations are all handled by exported variables and PATH statements, so it should be pretty portable, as long as the kernel and bootloader get done right (and all the system components, like OpenMPI, are available). Are there any major last minute warnings other than the general risk of loosing everything? <<shudder>> This machine is dual boot with Win2K3ServerEnterprisex64, but 12.1 GRUB is handling the booting. I guess I need a backup copy of menu.lst and check where my bootloader is installed (just in case) - then select the option for a system update install from the DVD?

atti@OS121:/usr/local> ls -l
total 397156
drwxr-xr-x  2 root root      4096 Jan  3 20:01 bin
drwxr-xr-x 10 root root      4096 Nov 16  2012 esmf_2.2.0r1
-rw-r--r--  1 root root   7877548 Nov 16  2012 esmf_2_2_0rp1_src.tar.gz
drwxr-xr-x 11 root root      4096 Nov 16  2012 esmf_2.2.2rp3
-rw-r--r--  1 root root   1615365 May 13  2012 esmf_2_2_2rp3_src.tar.gz
drwxr-xr-x  6 root root      4096 Oct 27  2012 esmf400rp1
drwxr-xr-x 15 root root      4096 Nov 16  2012 esmf_4.0.0rp1
drwxr-xr-x  6 root root      4096 Oct 28  2012 esmf_400rp1_openmpi
drwxr-xr-x  3 root root      4096 Sep  7  2012 games
-r--------  1 root root 382027195 Jan  6  2010 idl711linux.x86.tar.gz
-r--------  1 root root   5064299 Jan  6  2010 idl71sdf_HDF5_linux.x86.tar.gz
drwxr-xr-x  8 root root      4096 Oct 27  2012 impich2_141p1
drwxr-xr-x  2 root root      4096 Oct 25  2011 include
drwxr-xr-x  6 root root      4096 Oct 27  2012 inetcdf363
-rwxr-xr-x  1 root root      2618 Aug 19  2009 install
drwxr-xr-x  7 root root      4096 Oct 11  2012 iopenmpi_16
lrwxrwxrwx  1 root root        15 Jan  3 20:01 itt -> /home/patti/RSI
drwxr-xr-x  3 root root      4096 Sep  1  2012 lib
drwxr-xr-x  2 root root      4096 Oct 25  2011 lib64
drwxrwxrwx  2 root root      4096 Sep  9  2012 license
drwxr-xr-x 12 root root      4096 Jun 11  2012 man
drwxrwxrwx  8 root root      4096 Aug 27  2012 mpich2_141p1
drwxr-xr-x 15 root root      4096 Oct 27  2012 mpich2-1.4.1p1
drwxr-xr-x  3 root root      4096 Aug 25  2012 NCL610beta
drwxr-xr-x  3 root root      4096 May  4 23:44 NCL612
drwxr-xr-x  6 root root      4096 Sep  3  2012 nco421
drwxr-xr-x 14 root root      4096 Sep  3  2012 nco-4.2.1
-rw-r--r--  1 root root   5165714 Sep  3  2012 nco-4.2.1.tar.gz
drwxr-xr-x  4 root root      4096 Aug 15  2012 ncview-1.93h
drwxr-xr-x  6 root root      4096 Aug  5  2012 netcdf363
drwxr-xr-x 18 root root      4096 Oct 27  2012 netcdf-3.6.3
drwxr-xr-x  6 root root      4096 May 19 21:04 netcdf430_C
drwxr-xr-x 23 root root      4096 May 19 20:52 netcdf-4.3.0_Clib
-rw-r--r--  1 root root   4735397 May 19 20:48 netcdf-Clib-4.3.0.tar.gz
drwxr-xr-x  7 root root      4096 Aug  5  2012 openmpi_16
drwxr-xr-x  9 root root      4096 Oct 11  2012 openmpi-1.6
drwxr-xr-x  8 root root      4096 Jan  1 18:10 parallel-netcdf-1.2.0
drwxr-xr-x  9 root root      4096 Jan  1 17:35 parallel-netcdf-1.3.1
drwxr-xr-x  6 root root      4096 Jan  1 18:11 pnetcdf120
drwxr-xr-x  6 root root      4096 Jan  1 17:45 pnetcdf131
drwxr-xr-x  7 root root      4096 Jul  1  2004 qslim-2.1
drwxr-xr-x  2 root root      4096 Oct 25  2011 sbin
drwxr-xr-x  5 root root      4096 Sep  1  2012 share
drwxrwxrwx  4 root root      4096 Sep  9  2012 src
drwxr-xr-x  3 root root      4096 Sep  3  2012 udunits11211
drwxr-xr-x  3 root root      4096 Sep  3  2012 udunits-1.12.11
drwxr-xr-x  6 root root      4096 Sep  3  2012 udunits2124
drwxr-xr-x  6 root root      4096 Aug 15  2012 udunits-2.1.24
drwxr-xr-x  7 root root      4096 Oct 12  2012 vapor-2.1.0
drwxr-xr-x  8 root root      4096 Jul 31  2012 vapor-2.1.0-Linux_x86_64
drwxr-xr-x 14 root root      4096 Jul  4  2012 vis5d+-1.3.0-beta
patti@OS121:/usr/local> 

You already seem to know the drill.
But whatever… Still Backup

Or change the standard set of repos to 12.2 and ‘dup’ it
Disable other repos (But include nvidia if you are using it)
You can actually try and just see how it responds to your ‘dup’ request