What is the correct way to set post processing material at runtime?

I am getting:

Warning  Blendables  - the native property is not tagged as BlueprintReadWrite, the pin will be removed in a future release.

When trying to set post processing blendables in such a way:

What would be a correct way of doing this that doesn’t generate a warning?

Its been like that since I have a memory of it. This warning comes out with all structs properties that are not marked with that decorator in C++ (BlueprintReadWrite). I don’t know of other way for doing this, but I don`t think it will change either. If you find another way please share with us. Cheers!