Howto update-safe change Grub2 default to windows

On debian (ubuntu / linux mint should work too) this is quite simple. Grub2 takes menu entry names as default options. This can be done here:

# filename: /etc/default/grub
# search for or add if it not exists:
GRUB_DEFAULT='Windows 7 (loader) (on /dev/sda1)'

Your install might differ. GRUB_DEFAULT takes the menu entries from your grub.cfg usually placed in /boot/grub/

grep -o "menuentry '.*'" /boot/grub/grub.cfg

And here it is:

menuentry 'Windows 7 (loader) (on /dev/sda1)' --class windows --class os $menuentry_id_option 'osprober-chain-XXXXXXXXXXXXXXXXX'

All what is left to do is update grub as super user: