That is...

Un-create a mode
    /set mode <mode> -delete
Un-retaining a mode
    /retain mode <mode> -delete
Un-setting an editor
    /set editor -default
    /retain editor -default
Un-setting the start-up
    /set start -default
    /retain start -default

... also ...
No start-up
    /set start -none
    /retain start -none