You could make Kodi run as a different user. Open dietpi-services, select kodi, select Edit, and add User=yourUser below the [Service] line. In case, you need to add the user to additional groups to grant access to GPU and audio devices:
usermod -aG audio yourUser # ALSA/audio device access
usermod -aG video yourUser # General video/X server access
usermod -aG render yourUser # DRM access, required on RPi and Odroid N2+C4
usermod -aG dietpi yourUser # To access media/downloads with default permissions on DietPi
Probably more is required to make it run fully featured not sure. Report back how it works, I anyway plan to run Kodi as own user “kodi”, group “dietpi” and UMask 002 in the future to limit it’s permissions to what is required and allow easier cross access for other users.