We're planning to roll-out the modern library experience to a customer in batches instead of switching over all at once. So we do not want to switch on the modern experience from the SharePoint admin center level but control this on site (web) or Site collection (Site) level.
There is documentation on how to do this through PowerShell/CSOM but this doesn't have any effect. I've tried to switch on and off the mentioned features but it doesn't seem to have any effect to either way. https://support.office.com/en-us/article/Switch-the-default-experience-for-lists-or-document-libraries-from-new-or-classic-66dac24b-4177-4775-bf50-3d267318caa9?ui=en-US&rs=en-US&ad=US
I tried without luck the script from this question Disable modern experience for a site collection where the answer was provided as form of extended script based on office.com's sample.
Is this somehow outdated information and is there some alternative way to achieve this?
Edit: Per newer article at https://msdn.microsoft.com/en-us/pnp_articles/modern-experience-customizations#converting-existing-sites-to-modern-team-sites they say switch is not possible but previous instructions still seem to exist so it is a bit conflicting.