Change/re-use root partition in ec2 instance

I start a new machine (with flag "don't destroy volume" enabled), configure everything (save information), and then I turn it off. For example:

/dev/xvda1: LABEL="cloudimg-rootfs" UUID="27161562-4167-40e6-90ad-0c63a3b9b766" TYPE="ext4"

Later, I start another machine and I attach this volume as sdf (/dev/xvdf1). If we take a look at blkid:

/dev/xvda1: LABEL="cloudimg-rootfs" UUID="27161562-4167-40e6-90ad-0c63a3b9b766" TYPE="ext4"

/dev/xvdb: UUID="a3f4fe04-ecb4-47a8-96e3-1f921b82ea74" TYPE="ext3"

/dev/xvdc: UUID="a3f4fe04-ecb4-47a8-96e3-1f921b82ea74" SEC_TYPE="ext2" TYPE="ext3"

/dev/xvdf1: LABEL="cloudimg-rootfs" UUID="27161562-4167-40e6-90ad-0c63a3b9b766" TYPE="ext4"

Well, one month ago, I used this command:

sudo tune2fs -L 'test' /dev/xvda1
sudo reboot

and when I connected again, I was exactly as I had my first machine (it's using /dev/xvdf1 as root partition. Partition /dev/xvda1 is not used).

Right now, it isn't working any more. Any clue? Do you have any method I can use for re-use the HD like I try? I would like to avoid using snapshots/amis.

Extra: First machine is c3.large, second is c3.xlarge.