I'm not at all sure these will be the answers that you want, but here goes anyway.
1/ If the scientific method requires the making of predictions that are observable to our senses, & one of those predictions is that god can suspend & alter the rules of physics. Then surely god appearing and creating matter/energy in the form of a large planet nearby (for example) on request, represents a legitimate scientific test?
Having the capability of doing something and actually doing it are two different things. What you propose is not a test of the ability to do something, but of the intent to actually do so.
Matthew 4 (Mark 1 and Luke 4 as well) contains the story of the devil tempting Jesus. Jesus is asked to perform like a trained dog, to show off his powers. He refuses in each case. That does not show that he was incapable of any of those acts, but rather that he chose NOT to perform those actions.
2/ If something does not interact with our universe, how are we supposed to test its existence? Given this is a rhetorical question & the answer is that it cannot be tested. Then why should we accept the existence of something that cannot be tested?
The existance of GOD is a matter of belief. It is personal and as you say, not subject to testing. But there are vaild reasons behind such a belief.
While IMHO, some of what was posted in the thread was just plain silly, I can see GOD in the world around us. As we learn more and more about evolution, about physics, about cosmology, about biology and genetics, we find a beauty, an aesthetic sense to the underlying rules that seem to govern all interaction. As we learn more, at each step we are finding yet more detail behind and driving what only a moment before we thought the most basic. And behind that, there reamins the question of WHY. WHY did something that may have existed for all time, some primal singularity, change state?
While I fully support Evolution and the Theory of Evolution, support the evidence of the Universe we live in and those rules that seem to govern its form and creation, that still does not address the question of WHY.
GOD is the answer that I have found to the question of WHY.
Aslan is not a Tame Lion