Pedal stack height does not actually alter hip angle on it’s own. No matter the pedal height, it is the same distance from the top of the pedal while at the bottom of the stroke to the top of the pedal at the top of the stroke. That top of pedal distance to the other pedal top is exactly the crank arm length doubled, no matter how tall or short the pedal stack.
Low pedal stack DOES allow for lower saddle height, all else being equal, than a taller stack height. But we are talking about maybe 5mm delta, so not really notable, IMO.
Assuming you swap from a tall pedal stack to a low pedals stack, adjust saddle height to match that drop, and leave the rest of the bike alone, this will decrease saddle to bar/pad drop, which effectively opens hip angle a tiny bit. But that’s lots of conditions, and what people actually do as a result of lower pedal stack can and will vary. If they drop the bars to match the saddle drop (not uncommon), they kill the “opening” aspect entirely and just lowered the rider as a whole.