If I understand correctly, you are asking if a meteor impact could (i) slow the Earth's rotation on its axis or revolution around the Sun enough to account for the 8 to 12-fold decrease in longevity of human-kind measured in Earth days/years; and (ii) cause 40 days of torrential rain, resulting in sufficient inland flooding to float a large wooden boat.
An asteroid hit near the equator big enough to slow the rotation rate by a factor of 8 to 12 would be, literally, an Earth-shattering event. Assuming a glancing impact at a typical asteroid speed of 25 kph and negligible mass ejected into space, I estimate a mass of around $\frac{1}{100}$ of that of the Earth - about the size of the Moon, roughly 3000 km in diameter.
Such an enormous impact would be like the collision of 2 raindrops. The thin crust would be vaporised, the viscous mantle would be broken open and would mix with the liquid core, the solid core might even be ejected. The Earth undergo large distortions and oscillations, and significant portions would be ejected into space, possibly creating new moons.
Getting into a wooden boat wouldn't give Noah any protection at all. Except for a few hardy microbes travelling in/on space debris, all life would be extinguished. No oceans or atmosphere would remain - but an atmosphere of heavy volcanic gases would probably build up as the Earth cooled, which could contain significant amounts of water. After several thousand years of cooling, the Earth would still be a barren, uninhabitable rock. It would take millions of years for animal life to get re-established.
Yes, the effects would be instantaneous - within days or weeks, not spread out over hundreds or thousands of years to make the impact survivable. A series of 3500 smaller asteroids of 50 km diameter would cause far less destruction, but could not add up by chance to the same effect on rotation or revolution rate.
An asteroid that big would be as spherical as the Moon. Another shape (eg spear-like) would make little difference to the outcome. In order to get the same change in linear or angular momentum, its mass and the amount of kinetic energy dissipated by the impact would be about the same. A 'spear' would not penetrate very much deeper than a 'sphere' (see Rod Vance's answer to your qn How an asteroid enters the Earth make a completely different outcome?).
A meteor hit on the polar ice cap won't have much effect on the rotation rate, although it is possible that a glancing impact could vaporize enough ice to cause a world-wide deluge without causing global devastation. A large polar impact could knock the Earth off its axis, but not without similar devastation to that described above.
The following video simulates the effect of a 500km wide asteroid hitting the Earth head-on. It is estimated that the Earth has suffered 6 such hits during its 4.5 billion year history, plus the larger collision which created the Moon.
https://www.youtube.com/watch?v=bU1QPtOZQZU
