Earth is not symmetrical nor a rigid body. The axis of rotation is changing all the time and so does the magnetic axis (if we assume there is one, when of course Earth also isn't a regular magnet by any means). Now, with all due respect the reason we know this is because we have telescopes and satellites and all kinds of measuring instruments none of which are people living on floating glaciers.
At any rate, the kind of spin that would generate enough centrifugal force to actually counteract gravity on Earth would probably shape it into more of a disc in the process. There is a measurable difference in weight of equal mass between spots on the equator as opposed to the poles, but they are very small differences indeed... The kind of collision a change of that magnitude would take would probably break the planet into pieces anyway, whether they find their way back together afterwards or whether they'll even keep any sort of solar orbit. We are also rather on an edge of our sun's habitable zone (vague though that term is becoming), so there is some room for changes to our orbit that might improve Earth's support for life. Of course a rapid acceleration would destroy up to all of it regardless, but as mentioned before, that's not the only conceivable way changes of this sort may be induced.
Better to leave questions unanswered than answers unquestioned
