@LenAsh, @slaphead20, @ficti0n851
Hehe, yeah, I'm stuffed without a cable
I lost it recently and I'm the only one with a recent phone. All my family members' phones use different cables.
Anyway, I managed to borrow a friend's cable and am currently downloading drivers for the S3. Once that's done I will use ADB to set the file permission and try rebooting my phone, failing which I will restore the backup build.prop, set permissions and reboot the phone. Failing which... well, maybe I'll reflash the stock firmware (I managed to find out the exact build details btw!
I'll keep you posted, thanks for taking the time guys
ADB was a success! I got in and changed the permission to 644 and rebooted, done! Funny thing was that /system/build.prop file was not even there, there was only /system/build.prop.bak. I was not able to find my original backup on the sd card, but I copied the .bak file (probably generated by ES FE) and set its permissions and that worked. And now I have also have the software keys!
Thanks for your comments guys. This was fun!
For anybody else who has the same problem, I did it using the commands in these great ADB guides:
Also, how do I edit the title of the topic? Want to add a [Solved] tag.