Comment # 6 on bug 1155824 from Takashi Iwai

You don't have to register the repository just for testing a kernel package.
The easiest way is to download kernel-default.rpm from the OBS download URL,
e.g.
  http://download.opensuse.org/repositories/home:/tiwai:/bsc1155824/standard/

then install the package with zypper in.  You might need to pass --oldpackage
when the release number is smaller, e.g.
  zypper in --oldpackage kernel-default-*.rpm

There you'll be asked about the signature, and continue with "ignore".

But, before performing the above, I recommend you to increase the number of max
installable kernels in /etc/zypp/zypp.conf.  Edit /etc/zypp/zypp.conf and add
more entries of "multiversion.kernels" line, e.g.
  multiversion.kernels = latest,latest-1,latest-2,latest-3,running

This will keep more kernels on the system, and prevents to wipe out
unexpectedly the good one.