It's possible to generate your own error message like "blockes by opnwrt"? Otherwise, only the standard browser information that a connection cannot be established appears.
Greetings
Neuro
You can do a redirect of the sites you're blocking, certs would be a problem though, if you try to redirect https.
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There was a nice feature in pi-hole which was able to generate your own error message...that was the backroud of my question...
Pi-hole uses dnsmasq, so does Openwrt.
The custom block page have been dropped though.
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Yes..."was"... 
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https/ hsts makes that effectively impossible.
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