Can I just write a script which will install all the RPM's present in SLES 11 SP2 on my SLES 10 SP2 system
I'd recommend that you don't do that.
(...) there is no direct upgrade path from SLES 10 SP2 -to- SLES 11 SP2
Upgrading directly is not supported, but you can upgrade step by step as explained in https://www.suse.com/releasenotes/x86_64/SUSE-SLES/11-SP2/#id326453:
9.1.8. Upgrading from SLES 10 (GA and Service Packs) or SLES 11 GA
There are supported ways to upgrade from SLES 10 GA and SPx or SLES 11
GA to SLES 11 SP2, which may require intermediate upgrade steps:
SLES 10 GA -> SLES 10 SP1 -> SLES 10 SP2 -> SLES 10 SP3 -> SLES 10 SP4
-> SLES 11 SP2, or
SLES 11 GA -> SLES 11 SP1 -> SLES 11 SP2
I've found out that the best approach for upgrading SLES10 SP2 -> SLES10 SP3 -> SLES10 SP4 is to boot off the corresponding SLES DVD and select 'Installation' and then 'Update this system'.
After upgrading to SLES10 SP4:
Delete all zypper repositories.
Configure zypper to use the new SLES11 SP2 repositories.
Download the new RPM packages:
zypper -n dup -l -d
To minimize the impact of a network outage it is always a good idea to download the RPM packages first (also when updating:
zypper up -d and then
zypper -n dup -l
Now that SLES11 SP3 is out and you can follow the exact same procedure replacing SLES11 SP2 with SLES11 SP3.
Why do vendors don't support direct upgrade path?
They probably want to miminize the number of possible upgrade paths to reduce documentation and simplify support on their end.
Note that not supported doesn't mean that it won't work: I tested upgrading SLES10 SP3 to SLES11 SP3 without any problems...