Edit 1: So I tried to generate a Material on a plane mesh which i could scale under the acor. But the border itself got scalled too. so thats no solution…
Edit 2: Read about procedural meshes. But wouldnt there be the same problem with the scale as the material?
I would use a decal within a blueprint that you call when needed. You can find additional information on decals here:
Effectively, you create a deferred decal material, apply it to a plane mesh that is located within a blueprint. The blueprint is then called whenever needed and displays the decal. It is one of the more efficient means to accomplish the goal you are looking for.