Moving /boot partition without messing up the system

The boot sector needs to find the boot partition, after that the boot loader goes off the partitions, it doesn't care were they're located at on the drive.
I'm assuming you're using gparted live by the screen shot. After resizing you'll need to from the shell:

1. Mount your relocated root partition containing the boot directory
2. if /boot is a separate partition mount it in the root partition mount
3. Mount the /dev to the dev directory in your root mount using the --bind option
4. Chroot into the root mount
5. Run grub-install or liloconfig to reinstall the boot sector