OK. Have figured it out.
- After having first created the silent install via
K-Lite-codec_pack-XYZ.exe -MakeUnattended
... and then running the batch file that gets created ... that's all there is to it!
Newer versions of K-Lite can be comfortably installed on top of old ones, though care should be taken in upgrading from very old K-Lite version. For more information about this point, see this relevant section of the FAQ.
It's also possible to run a silent un-install first. As well as removing K-Lite via the Control Panel, you can also run the uninstall executable, as described here.
Comprehensive blog posting with sample Visual Studio project can be found here: