Not sure this will work out.
I mean *of course* serverside there is data concerning monster level and a whole lot more of data.
The thing is that such information is *not* sent to our clients with the rest of the data that gets sent on communication packets, which means our clients will not be able to display monster level. It's not like (it's the case for several other info, for instance) it's part of the plenty information that DOES get sent but it's just not displayed.
Monster level just isn't sent.
The only moment when such info is sent to clients is when you use the check command, hence unless they change packet data (but in the past they already said they had no intention to do so for other things) that's not a kind of information that they'd be able to let us see just by flagging it as "viewable", they would have to change more core stuff for that and honestly I don't see it happening.
Changing the message while we check to a "The monsters looks to be level XX, it's a decent challenge!" is instead quite possible, and as a matter of fact you can already do that with third party addons, which implies it wouldn't take them more than 30 minutes of single person work to do that.