Can i modify the transform of InstancedStaticMesh after i AddInstance

Hi, i making some kind of like starcraft map editor, where u can have some simple editing like level the level and add borders around them.
Those borders i use only 3 static meshes to make, so i want to use InstancedStaticMesh to save the draw call, but then i need ability to remove border, and since i cannot do that so i’m thinking of can i edit the transform of instance mesh ?
And do we have some way to like combine 2 static mesh with same material to 1 static mesh.

Here the borders i made from Unity.

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Sure, you can. The only thing you need to know is the exact location of your instance. Once you found it, you may set new FTransform for it.