Custom safe area masks

[smbell]

Much to our dismay, we're having to deliver a lot of projects in 9x16 in addition to the usual 16x9, thanks social media . Being able to preview a 9x16 aspect safe area would be extremely useful to evaluate our existing renders.

I see that there are a lot of presets under the safe area menu. Is there a way to edit these? If not, that would be amazing to have that ability.