Hello!
If i remember correctly, i learned that i can add a custom destructible damage model to my “pre-modeled wall with impact holes” destructible. I then learned that i can “crack” the wall model in blender (where i originally created it) with an… modifier?
So what did i basically do:
I think i cracked my wall into pieces with an modifier in blender. My “1 piece wall” mesh turned into… let´s say… 160 mesh pieces.
I then imported those 160 wall pieces as one mesh into unreal engine. I think.
And then i added the “160 pieces wall” as the damage mesh for my “1 piece wall”.
So whenever i damage my wall with the doorframe and impact holes (which i set as an destructible), the whole destructible model will switch to the “160 pieces wall model with the doorframe and impact holes”.
So basically this:
I shoot → “Wall with doorframe and holes” destructible → turns into “160 pieces wall with doorframe and holes” damage model (so basically the mesh changes to the 160 pieces model) → the custom hitbox for each of those 160 pieces comes with it → means that you can shoot even through the holes, after the original 1 piece wall mesh has been damaged. That means you can shoot off the wall piece by piece.
The only issue i encountered with this technique is, that it can happen that you will see little cracks on the 160 pieces model. It might look ugly, but it could be used as a look to signal or indicate that this wall has been damaged. So you may have to fix by slightly remodeling each piece. Also that means that the system will have to count more polygons and triangles to render.
If i explained something to obscure or confusing, you can find information on the custom damage model for an destructible inside unreal engine
and you can find information for the “cracking” modifier for meshes in blender
on YouTube.
I sadly 
paused my project since i replanned my life decisions, but i wish you a lot of luck and great success on your project! 
There is also something with an chaos thing destruction or something from unreal engine. Might also wanna look into that.
But yeah. Great success on your project and let me know if it maybe becomes an available game of some sort!!!