Jay To understand better what is going on in your first link,
First install Windows 10 then install DragonFly BSD take note of the slice you installed DFBSD, DON’T install boot0 ou bootblocks in the instaler, instead after it finished the installation drop to a shell by going to Live CD Utilities and execute the following command disklabel64 -B da0s5 (change da0s5 for your slice) to install the bootblocks that will be chainloaded by the Windows Boot Manager.
Wait if I change from disklabel64 to da0s5 then how does this install bootblocks? What does this command do and what is da0s5?
Do you have any idea how come just simply installing bootblocks screws up Windows and produces this error as I am trying to understand better what is going on?