What would happen to the universe if the physical constant of Big G was changed?
We would be in a very different Universe - probably one which wouldn't exist for very long.
G is a fundamental constant which relates mass space and time in our theories.
I do wonder whether the evidence for the existence of Dark Energy and Dark Matter, and all of that is a very open question at the moment afaik. Perhaps it could be explained by G not being actually a constant but a function of distance.
I won't fall into the trap of saying what the situation 'really is' but perhaps a variable G could give a model (for them as are smart enough) which does without Dark Stuff.
Separate names with a comma.