Installing LibreELEC 9.95.4 on Pi4 with PINN

I'm trying to set up the latest version of LibreELEC so I can use Kodi 19, and seeing as the Kodi package for Retropie is still on 18.6, I'm wanting to set up a dual-boot with PINN so I can have both LibreELEC and Retropie on. Unfortunatley, I can't quite figure out the process of changing the version to install within PINN and the "custom os" installation process is going a bit over my head. I've recompressed the image within the image.gz file into a tar.gz file using 7 zip, but I'm not sure where to go from here.

Is there an easy way to go about this?