We could always “throw” Mercury at Venus.
If you have the technology to throw something big enough at Venus that the collision would change it’s spin, you’d probably have the technology to change Venus’ spin directly, wouldn’t you?
Planets are big, folks. You can’t go knocking them around like billiard balls.
You could set off every nuke on the planet and the explosion would be ten million times smaller than the impact that killed the dinosaurs. And was an asteroid just 10 kilometers in size. And that didn’t change the Earth’s rotation by a measurable amount.
There’s mindboggling big, and then there’s the kind of energy it takes to move a planet, m’kay?
Well that’s what we were saying. :dubious:
There you go…use Mercury! 
Ok, so maybe that won’t work…
(At work, I have a reputation as a kludge-master – coming up with simple but ‘barbaric’ solutions that many times are cheap and actually work)
If the Venus day is so long, That presents a huge problem for Terraforming. How would plants survive? Even if you have mirrors to light up the dark areas, I imagine there are huge problems with weather/tempature/other dealing with 243 ‘day’ days.
No.
Well if you want to kludge it use the sun shades. You need them to keep average temperature down anyway. Have them “open/close” on a 12/12 hour cycle.
If you can send that many comets into the surface at 90 km/s, then you can send an equal number into some orbit thingy and let them drop onto the surface. They are cold – giant freezers.
The thing is, how long will it take the whole planet to cool down even today? Venus has been roasting at 800 degrees for millions of years. Very bad for the Venusian wine cellars.
Ah, yes, the 12,000 Km diameter Venusian blinds. Just pull the cord to open and close them…
What about scaling back the operation by just getting rid of part of the atmosphere slowing it’s rotation so it has a permanent night side that might be cool enough to live on?
No, if you’re going to sling any product from the Ford Motor Company at Venus, use the annoying “Zoom, zoom” kid. (Ford owns Mazda and Mercury, FYI). I don’t know if it’ll have the desired effect on Venus, but it’ll certainly improve things here! 
If there’s a serious overpolulation problem, there’s a simple science fiction answer.
You tell people that you’ve terraformed Venus, and get them to sign up for the trip.
Then you market Soylent Green on the side.
well no known ones. under our current understanding a faster then light particle would also be going back in time. could we interact with something the other way in time? i don’t think we could, it would just lead to too many paradoxes. any way if we can’t interact with them then faster light particles would not be currently experimently varifiable. sucks don’t it?
well maybe not, if someone made an expiremnt that made mass just seem to disappear that would be the best explination, and maybe proof for tachyons.