final class SomeClass
 {
-    protected const SOME_CONSTANT = 'some-value';
+    private const SOME_CONSTANT = 'some-value';
 }

<?php

use Rector\Config\RectorConfig;
use Rector\Privatization\Rector\ClassConst\PrivatizeFinalClassConstantRector;

return RectorConfig::configure()
    ->withRules([
        PrivatizeFinalClassConstantRector::class,
    ]);

Other rules in the Privatization set

• PrivatizeLocalGetterToPropertyRector - Privatize getter of local property to property
• PrivatizeFinalClassPropertyRector - Change property to private if possible
• PrivatizeFinalClassMethodRector - Change protected class method to private if possible