Whooooooooooaaaaaaaa That's a bit drastic- I know mods are really hard, but that doesn't mean you should deliberately fail them!
Why do you think you will get a lower second? if its because of essay results, don't worry too much- my essays were all crap for the first two terms because you have to get used to writing in a legal style, but i still did fine. it's also worth bearing in mind that tutors sometimes mark more harshly than examiners in an effort to try and make you try harder. You'll also find it seems much easier the second time round (i.e. when you're revising)- suddenly all the jumbled mess starts to make sense.
Even if you do get a 2:2, it doesn't mean you can't go into the law- you may find it more difficult to go into one of the top firms, but there are plenty of mid-range law firms with really strong, varied practises who would be glad to have you, especially with a degree from Oxford. You will still end up with a varied and satisfying practice and earning a good wage- the idea that a 2:2 is a symbol of some kind of failure is absurd.
Structure your revision: you're going to need to learn about 5 or 6 topics from each paper in order to be certain you're going to pass- pick things which are easier on the revision e.g. Sex offences, where you will have the statute in front of you during the exam and need to just make sure you know it all as well as you can. Don't try and learn all the cases, but learn patterns in the law. look at past papers once you think you've done a topic and write essay plans. You've 6 days left- that's 2 on each subject, which is enough to get some serious consolodation in.
If you fail one of your papers, you will have to take it again in the summer. bear in mind that you will have to keep up with your work next term and study for this paper and that the tutors won't have created any extra time, so you'll actually be worse off than you were this term. Your pass mark will probably be 50 too and you aren't likely to get any revision classes. you may still have to declare the fail on job application forms. I don't think there's any university rule that prevents you from deliberately failing, but bear in mind that if your tutors know that that's what happened they can make life pretty difficult for you.
I think you're being very short-sighted: this is a quick fix solution now near to the exams when you're worried and stressed, but will probably cause you endless problems in the long run. Oxford is a hard place to study, but if you choose to study here, you have to grit your teeth and get on with it. I think Mods are very daunting because they come so early and you don't really knoiw what to expect, but it will be OK and with some focussed revision, you can do it.
Good luck, and PM me if you want any more help.