https://en.wikipedia.org/wiki/Gravitational_constant#History...
But it does point at one measurement of G on cosmological timescales and distances from 2006:
https://arxiv.org/abs/1402.1534
There are other papers with similar measurements published in the past two decades.
That isn't a particularly fruitful approach since it doesn't permit any real discovery - it's rather brain-in-a-jar - but it is still something you have to assume away.
Since these operate in concert across the observable universe, and themselves involve various other interactions (elements, strong and week nuclear forces, gravity, speed of light, rates of hydrogen fusion, etc.), we can conclude that either there is no appreciable change in any of the underlying fundamental constants or that change occurs in a compensated fashion such that no net change is detectable.
The second fails Occam's Razor. The conclusion that the laws of physics appear to be similar throughout observable space seems robust.
This is, in principle, a problem. We unfortunately have no way to measure the speed of light in andromeda, unlike what we can here on earth, so we really have no idea if our astronomical models are wrong given the non-constancy of the speed of light in andromeda or elsewhere.
So, yes, in principle not being able to repeat science experiments everywhere in the universe is a problem. However, I think if one thinks a little less broadly, testing newtonian gravity in say, Italy and also in China shows at least across the Earth, the phenomenon is similar. Then, at least one can say, "certainly, gravity is the same in Italy and China, and perhaps across the surface of the Earth." That is a stronger statement than "gravity is this way in Italy." Ordering claims by "scientific goodness", we can say that
My point here is that even if one can't fulfill the extreme of testing theories everywhere in the universe, one can progressively prove stronger and stronger statements regarding the validity of scientific theories.Somewhere the LHC stands between "the SM is validated across the universe" and "the SM is validated at one detector at the LHC". Yes, it would be "better" if the Higgs was found at other experiments, but the current situation is "better" than if the Higgs was found at one detector there and not in any other. Repeatability, like everything in science, is not a binary step function but is some continuous function over the domain [0,1].
[0] https://en.wikipedia.org/wiki/Cosmological_principle