You can edit the vertices of a mask by selecting and moving them using AutoCAD grips.
You can add vertices to the boundary of an existing mask by selecting and moving a midpoint of a mask boundary segment.
You can use AutoCAD editing commands to move, rotate, stretch, erase, or scale a mask.
If you want to change how the mask affects the images that are outside the mask boundary, then you can change the mask properties, disable the mask, or convert a mask to image clips.