Most Linux installations put Grub on the MBR. Most times when Windows disables Linux boot what has happened is the Grub MBR has been replaced with the same legacy MBR code Windows initially installs. In such cases, changing the location of the boot flag would not help. Moving the boot flag would solve the issue if Grub had been installed on a primary partition instead of the MBR. This sounds like a case where the best course of action would be to boot the media from which you initialized openSUSE installation originally, selecting the repair bootloader option. Once a repair has been performed, you may be able to reconfigure openSUSE with Grub on a primary partition. Then when Windows update disables boot, moving the boot flag back would be a simple fix.