@thetraingoes As per https://retropie.org.uk/forum/topic/3/read-this-first, 3rd party images are not supported, since - as you discovered - each one has configurations that are non-standard for a RetroPie installation.
That being said, overlays/bezels are configured in RetroArch and you can disable them using the RetroArch GUI - bring it up with Hotkey + X while in game and disable the overlay/bezel. The image you're using might have specific RetroArch configs for the SNES core - see here. You can edit the SNES core configuration and remove the Overlay/Bezel lines for the SNES emulator.