GhostBSD hard drive non-touchable

I’m now going to install GhostBSD using UFS custom partitioning, I only have one hard drive named ada0, but I’m nowhere to modify or create partitions on this hard drive, even if partitions are removed I’m still nowhere to modify or create the new ones.
Full disk installations (regardless UFS or ZFS) are never considered to me, that I also have many systems like HBSD, Trident, Linux co-existing, finally I also have a non-system partition used for my personal data.
Any ideas for this tricky situation?