Xbian Beta 2 and BTRFS problem

[ErickP]

Hi, I have Xbian Beta 2 and BTRFS, a script that went bad modified my /etc/passwd and /etc/shadow files and they were renamed. They are still there but renamed.
The thing is that I installed a computer with Debian Wheezy in order to mount the SDCARD but Wheezy does not have the same version of btrfs-tools as the sdcard (sdcard has newer beta/unstable tools) so I cannot mount the btrfs partition.

what are my options?
I can boot my raspberry with the sdcard, but no operations can be performed because i cannot validate a user (no ssh for example).
What can I do to modify my cmdline.txt in order to boot in single mode?

thanks,

Terminal

sdhci-bcm2708.sync_after_dma=0 dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootflags=subvol=root/@,autodefrag,compress=lzo rootfstype=btrfs rootwait smsc95xx.turbo_mode=N elevator=cfq logo.nologo quiet noswap loglevel=0 mod_scsi.scan=sync partswap startevent=mountall splash nohdparm --startup-event mountall