3 Gorges Dam. Situation should be remedied soon.
I think you have the best take. If any shortening is possible, it would be from locking up large bodies of water, which wasn’t really a thing until 100 years ago.
If North and South America were ever separate, then I would think that their joining would have made quite a difference a long time ago.
You’re not wrong. The Earth is no different than a spinning figure skater tucking their arms in or spreading them out to adjust the speed of their spin. Mass changes in relation to distance from the equator has the same effect and it was reported the dam changed the length of a day as well as major earthquakes when tectonic plates moved.