Mute NotFoundHttpException from logs
Those should not be logged in web.log when running Craft 3.x, but rather in the web404s.log -- assuming you don't have devMode on (which it shouldn't be on for production...)

Vide: Zen and the Art of Craft CMS Log File Reading

Also should you really want to customize things, it's not hard to do with Craft CMS, check out: Creating a Custom Logger for Craft CMS