It’s not just a case of other students not getting priority though- if they fill all their places with penultimate year students, those applications won’t even be looked at. Many firms recruit predominantly from VSs, but most (barring small intake US firms) will still review direct TC apps and a large number of places will still be offered under this route.This statement could apply to any firm, though. Many firms recruit predominantly from vacation schemes and yet people still apply, especially if they're set on the firm and they're confident in their abilities to succeed on a Training Contract. People still get hired, even if they haven't gone through the vac scheme route (how else would firms fill vacancies if the vac scheme candidates weren't all up to scratch?). Absolutely nothing is lost here other than a bit of time and energy spent researching the firm and writing an application, but that applies with every firm.
That's particularly true here. As other people have said on this thread, they're not expressly excluding post-penultimate year students from applying. They're just making their ordinary application process more transparent. Many post-penultimates have secured TCs at CC by convincingly showcasing their skills, abilities and interest in the firm. That will equally apply this year, and it wouldn't surprised if a decent number of non-penultimates still get taken on for a TC.
If OP is absolutely set on Clifford Chance then they are absolutely not wasting their time by applying to the firm, and their application will probably be looked at. People should definitely be aware that non-penultimates don't get priority but it shouldn't completely put them off, and it definitely isn't a waste of time to do so.
I think the video CC have published with the head of Grad Rec effectively goes as far as telling non-penultimate year students not to bother applying without actually saying those words- in their own words, these applicants will have very little prospect of success.
Of course if others are absolutely desperate to work at CC and still want to apply, they should. But I’d be astonished if the firm recruits many (if any) non-penultimate students this cycle having gone out of their way to advise them not to apply. So there will be an opportunity cost in terms of another application that could have been made to a firm that is happy to recruit anyone and treats all apps the same.