Is there a possible way to snap along global axis when using custom transform axes? For example, open Blender, delete default cube, and add 2 planes. Don’t move any, just rotate one of the planes 45 degrees along the Y-axis. Now, with the face selected in Edit Mode, Ctrl+Alt+Shift to create an orientation based on the face. Select the top two vertices of the plane, which are above the level plane. Slide them along the face using the custom axis. I want to position these so they are vertically in line with the level plane, while keeping the original exact 45-degree rotation.
In reality, if I was presented with a scenario as above, I’d just subdivide. But this is just an example, I’ll be applying this to much more complex examples.