On the possibility of creating an experiment to test cause and effect between awareness and existence, this is a wicked challenge that has been studied pretty comprehensively at least by some of the more adventurous science initiatives mentioned earlier, also seeking a solution.
I haven’t spent a huge amount of time thinking about it, as I don’t believe I would get any further than they.
The problem is, if we do manage to change reality, everyone primed to witness the effect is left behind in the previous reality. In their world, the test failed. In the new world, no-one was primed to witness the results, so would be oblivious to a positive outcome. The only one who would know for sure reality has been changed is the one who actually made the change… and I guess… as you say; karma.