Not sure what exactly you want to achieve, but screen settings including skin can be found in envarc:mui/screens.txt.

For changing wallpaper you can use Ambient ARexx commands e.g RXCmd AMBIENT "LoadBackground RAM:butter.png MODE=TITLED TYPE=desktop". You can find some more ARexx commands in Ambients docs, also worth to check the MorphZone wiki.

Sbar modules settings are saved in envarc:mui/screenmanager.cfg and .prefs