"Dark enough that they can still sell navy merchandise. Dark enough to stand separate from the throwback gear, so the Brewers can still sell all the throwback merch they want. But still bolder, more vibrant, more blue than the boring navy."
This is from me knowing what New Era has availability wise for cap fabrics so what you're proposing is using Dark Royal which is essentially Dodger Blue for reference (Dark Royal is what Dodgers and Rangers use for their cap colors).
With that, the Dark Royal wouldn't really match with the current Light Navy merchandise. Might not seem like a big diff based off the pantone swatches you posted but go look at a Dodgers hat in person and it'll be a lot more evident that it's def not close enough to match with Light Navy.
So in short my point is for this concept, it'd ideally would just have the Brewers hypothetically making a full switch to Dark Royal across the board (not just for the caps) and rolling out new matching merchandise/uniforms since pairing this hypothetical Dark Royal with the current Light Navy wouldn't go together.