How to edit an iphone backup and then restore using it?

I need to remove 4GB of old sms attachments, i want to open my backup, delete the sms attachments and then restore my iphone using that backup.

i have an iphone 5, iOS 6.0.2, MacBook Pro, ideally i want to do this without jailbreak

Added (1). Thanks, trust an apple employee to say that lol: D

NO WAY… You can only restore the whole thing and then delete all the attachments 1 by 1. If you even try going in to the back up folder you will for sure damage the whole restore and not ever be able to restore again.

I want to as well. You can view your data with iPhone Backup Extractor but that doesn't help me cuz I need to EDIT the files.