Comment # 21 on bug 1200544 from Takashi Iwai

The previous kernel is still kept on the system after installing a new test
kernel, and you can choose which kernel to boot at GRUB menu, so there is
little risk.

At best, download kernel-default, kernel-default-extra and
kernel-default-optional rpm packages from the repo, and install those via
zypper install
  % zypper install kernel-default*.rpm
You might need to pass --oldpackage option to zypper install due to the nature
of a rpm packaging.

Once after testing, you can uninstall those package again via zypper rm.
  % zypper rm kernel-default-5.14.21-150400.1.1.g203aa60
(which will uninstall all three packages in a shot)