Decals: How to resize them

Hi everyone, I’m a Blender user and I’m using UE4 to build things with. I build my meshes in Blender and I export them to UE4.

Unfortunately, my wall ‘Blender decals’ (they are called image plains in Blender) cannot be imported into UE4.

Here’s my question: how do I resize a decal to make it have the shape of a triangle, for example. I know in Blender if you want to resize a cube and form difference shapes, you can resize the edges and make it look different. In UE4 I can only change the shape of my Decals to be either Rectangles or Squares. How do I resize the shape of my Decal Cube to make it a triangle, for example!

Is there a way to resize only vertices/edges?? Thankssss