How to change default Discourse theme via CLI?

just upgraded discourse from 2.0.0.beta4 to 2.0.0.beta5 and now the page does not load.
browser console gives some error about my slick gallery component which i have set as default theme.
now i tried to access /admin/ but here i get the same result.
i have alread read How to change default Discourse theme?
but as said, i cant access discourse administration.
how could i change the default theme on cli?

You can use safe mode to access the site if you have an issue with a theme/plugin:


thanks for the hint!
i think this should be stated in installation guide and in guide for how to add plugins/themes. :slight_smile: