If a K1.5 wanted to do that just for shits and giggles, is there a viable way to slow down or speed up orbits of rocky planets? Like, wouldn't they be shooting a bunch of mass out of their system to even attempt this? If one could build a Dyson sphere, is that more difficult or less difficult than engineering a system like this? The sphere/swarm has some absurd amount of mass all in a very uniform orbit around the sun, and most of that mass didn't start there... so it sort of seems like it's equivalent (but if so, they're much closer to K2 than K1).
There's some principle that for a chaotic system, if the accuracy with which you can measure it is smaller than the largest perturbations you can make to it, you are willing to wait many Lyapunov times, and you have enough compute; then you can control the system. With this after a few dozens of millions of years you could control the small bodies of the solar system using relatively small thrusters and a big radar installation, and then put them all on aldrin cycler orbits to move momentum between the larger bodies.
> is there a viable way to slow down or speed up orbits of rocky planets?
You can fly something massive near a target planet, while using some kind of engine to keep a distance. Gravity will do the rest. It may take some time of course, but all you need is to do maintainance on an engine regularly.
> Like, wouldn't they be shooting a bunch of mass out of their system to even attempt this?
It depends on a type of an engine. If you use solar sail for example it is not the mass but light will be thrown out.
> one could build a Dyson sphere, is that more difficult or less difficult than engineering a system like this?
Sphere seems to me more difficult. Not in a sense of energies involved, but from a standpoint of engineering.
