I've been through this before twice, so here is my advise based on my own experience:
1. back up your machine with Time Machine - you'll need the backup for step 1 below
2. buy a new identical (or current model) macbook the day of, or the day before your Genius Bar appointment
3. bring new macbook home, use the TM backup and restore it to a working state that matches the old machine. Take very good care of the new machine - no spills, scratches, drops, theft etc., you don't want to be stuck with it
4. bring your old macbook for the genius bar appt - you will refuse to identify which keys are malfunctioning, making them put "random" or "all" on the work order to basically force the repair depot into replacing the topcase entirely otherwise they will try and repair individual keys and you'll be back to square 1 in no time
5. watch the clock - you have 14 days to return the "loaner" - the repair should take about 7 days max, but usually around 5, but with everyone rushing in with their defective keyboards, it could go to 10-12 days
6. keep your new/modified files on icloud or dropbox during the repair time so you can sync them back to your old machine quickly and easily - you don't want to do a backup of the loaner and restore to the old machine, that just creates complications
7. follow the process to deactivate itunes, log out of Icloud, and wipe the hard drive carefully before re-repacking your "loaner" and take it to the Apple store to return at the time you pick up the old machine....if you suffer from a guilty conscious, which you shouldn't be when playing hardball with a publicly traded corporation, you can return the "loaner" to a different Apple Store from the one where you will pick up the repaired one. Apple will just test the "loaner" and sell it in their refurb store - the hit they take on the value is punishment for putting out a defective product in the first place and refusing to acknowledge how widespread the defect was.
I know some "super fans" might howl in disgust about doing the buy-and-return loaner thing, but there is nothing wrong, immoral or illegal about it - and it's not like other customers aren't doing it either. Since we can't have real loaners, and some of us cannot be without our computers for 5-10 days as they are absolutely needed for business, this is the only realistic option.