Musk has a lot going for him, the re-ignitable rockets and thrust control for example are ground breaking stuff - no one has pulled it off before and it has a significant potential.
JFC.
Here are two examples, since you refuse to believe that restart and throttling have been around for a while:
RL-10 - 1959 (Atlas V and Titan Centaur/Delta IV/Saturn I/DCX VTOL lander) - RL-10 can throttle from 104% thrust to 8% thrust - the best range of any engine, far better than SpaceX Merlin engines. Multiple restarts.
J-2S/J-2X 1964 and 2007. S and X variants both add throttle capability to existing J-2 engine used on Saturn V. Base J-2 had restart capability.
If you want just throttling, many more engines are capable of that. Here are a few just off the top of my head:
SSME/RS-25
RD-171
RD-180
RD-181
RS-68
Hypergolic or monopropellant engines have restart capability built in and are often throttleable as well, and there are too many of those to list. Those are already used for your pipe dream of satellites with manuvering systems, as well as some rocket upper stages, with notable examples such as the Apollo CSM engine, the Lunar Module Descent Engine, the Lunar Module Ascent Engine, the Space Shuttle Orbital Manuvering System engines - actually a new generation of the same engine used on the Apollo CSM - Russian transfer stages such as Fregat, and many more.