I think he might be sarcastic. There is no known method I know for measuring the rotational period of extrasolar planets, without having enough observational power to defiantly notice the astronomical engineering required to alter an inhabited planet’s rotation rate.

Actually I think if we follow the current trend in technology advances in astronomy, we will definitely be able to measure planetary rotation well before we have the angular resolution to spot anything of consequence on an exoplanet. We currently have the technology to measure stellar rotation bia Doppler shift. https://en.m.wikipedia.org/wiki/Stellar_rotation

This technique will definitely be applied to exoplanets as the angular resolution and spectroscopic sensitivity are improved. In fact, improvements to both if these numbers are being relentlessly pursued by a veritable army of scientists around the world.

Spectral broadening only needs one pixel, and enough spectral sensitivity that the broadening isn’t entirely in the margin of error. We are pushing For ever more accurate spectral sensitivity as we try to use Doppler measurement to hunt for exoplanets.

Meanwhile the ongoing efforts to obtain greater angular resolution, has basically been one of the core pursuits of the astronomical community for centuries. We are building massive telescopes and advanced compensation systems in the form of adaptive optics to get the very best out of these telescopes.

So yeah I think we’re going to have rotation rate measures before we see much more than a pale blue dot.

"You see that big city past that mountain range? Use it as a marker to measure the planet's rotation."

If we measure this city's position then we'll know if there's life on the planet.

You get the joke.

In the Three Body Problem series by Cixin Liu, the orbits of planets and moons in the solar system are altered to make colonization and terraforming easier.

Wrong. In the book they build the bunker stations behind Jupiter but NOT in orbit of jupiter or its moons and even that station keeping takes a tremendous energy.