dual boot: Win10 after Ubuntu (and getting back into my pc-bsd partition)

Hi,

I found an old thread outlining how to do a clean Win7 install alongside existing Linux installation(s). Basically, make sure the target partition is already in NTFS, and that you're in legacy/BIOS mode. And save your GRUB config somewhere so it can be reinstalled.

Is that still accurate with the Win10 installer? I have
- a recent notebook with UEFI boot disabled
- an SSHD with GPT pmap, 200Mb EFI partition first, with 1 free partition I could use for Win10 evaluation.
- a bootable USB thumb drive with last week's Win10 iso bued onto it.

I used that drive to upgrade a notebook's Win7, and was pleasantly surprised to see that was an almost perfectly transparent exercise. The Linux partitions on that rig weren't touched, and I didn't even have to reinstall GRUB (result: it still offers me an option to boot into Win7 )
That disk has an MBR pmap though, and also has a dedicated recovery partition (which was updated).

As a bonus question while I'm at it: does anyone have a good suggestion on how I could get grub to access my PC-BSD partition? Following the suggestions for a tailored etc/grub.d/40_custom only gives me a loader error that `/boot/loader` doesn't exist.