After downgrading to El capitan to test if my MBP mid-2010 would be faster ( which proved to be not significantly so), I decided to upgrade again to High Sierra, but I have found out that I cannot use my earlier downloaded High Sierra Installer to clean install it through a USB stick.
The createinstallmedia works, but I get failure when I run the installer.
When I removing the installinfo.plist file I get “This copy of the Install macOS High Sierra.app application is damaged and can't be used to install macOS”
The only solution is to upgrade it through a 20Mb installer from app store. Still, I am puzzled as how to do a USB clean install. Any ideas would be appreciated.