I need to resize my ext4 /home partition to make space to my boot partition before it. The thing is to do so I need to change the start sector of my home partition (the boot partition is extended on following space not on preceding space so the start sector of my boot partition remains unchanged). Is there any risk moving the start sector of my /home partition? I have my /home partition inside an extended partition.
There is always a small risk something could go wrong when you resize a partition so you should back up your data first.
Otherwise you will need to boot a live CD and resize your partitions in steps.