RGUI cannot be used to change core specific settings. If we enable save_config_on_exit configs/all/retroarch.cfg will be overridden with core specific settings like libretto core, key bindings and shader settings. configs/<emulator>/retroarch.cfg will not be changed.
Some changes are necessary to save only the core specific tetrarch.cfg:
add #include "$rootdir/configs/all/retroarch.cfg" to every configs/<emulator>/retroarch.cfg
If you start a libreto/retroarch core like pocketsnes or pscx_rearmed you can open a GUI (RGUI) with “F1” or with a “input_menu_toggle_btn” or an “input_menu_toggle_axis”. It is possible to change video, audio, input and path settings. Furthermore it is possible to change drivers. But your changes aren’t persistent. Your new settings will not be stored because save_config_on_exit = "false".
It is a good idea to disable this option at the moment. Otherwise the main retroarch.cfg will be overritten (/configs/all/retroarch.cfg). If i change something in pocketsnes, no other emulator core should be influenced. For example, if rewind can be used with nes/mastersystem cores it slows down pscx_rearmed.