I'm trying to triple boot Hackintosh, Windows and Ubuntu and I already have the GRUB bootloader installed on my whole hard disk. Ai already have Windows and Ubuntu installed and I've made a partition for the Mac so as I've understood from tutorials since the hackintosh will overwrite the bootloader I need to have a bootloader installed in /dev/sda4 whch is where I have Ubuntu installed so everything would work in the end after the hackintosh overwrites grub. How can I do this without starting completely from scratch (backing up, erasing whole hard disk, installing Windows, installing Ubuntu and specifying during installation and in the end installing hackintosh and so on)?

Thank you