New Macbook Pro - remove "high sierra", install "sierra" How do I get past the "do not enter" traffic sign that stops me from installing "Sierra" instead of "High Sierra"?

I booted into rescue mode and deleted the original "High Sierra" installation, but booting from the USB stick with the "Sierra" installer on it still gives me the "no".
If your MacBook Pro came preinstalled with macOS High Sierra, then you cannot downgrade to older OS as Apple restricted it. You have no other choice. You have to live with it.