I'm going to talk about Earth below, but since you say "an Earth-like planet", consider that just an space-saving measure.
Take an Earth-like planet, about the same size, composition and gravity.
Huge (say 500 kilometer diameter) asteroid strikes.
Well, as it's said in the movie, oh shit - there goes the planet.
An impact crater is:
an approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the hypervelocity impact of a smaller body with the surface.
The "approximately circular" part means that by definition, for an impact crater to form you need a more or less head-on collision. You can't simply "scrape" the target body, even if that counts as an impact, because that will create a very much elongenated shear rather than a circular depression which thus is not an impact crater but rather something else. This would appear to rule out an event similar to that described by the Moon's origin Giant Impact hypothesis, since that body didn't hit the Earth directly but rather scraped along the surface. Borrowing from the former linked page:
Computer simulations show a need for a glancing blow, which causes a portion of the collider to form a long arm of material that then shears off. The asymmetrical shape of the Earth following the collision then causes this material to settle into an orbit around the main mass. The energy involved in this collision is impressive: trillions of tons of material would have been vaporized and melted. In parts of the Earth the temperature would have risen to 10,000 °C (18,000 °F).
In our solar system as of today, a reasonable point of comparison to what you are proposing would appear to be Saturn's moon Mimas. Mimas has a diameter of just under 400 km and an impact crater (Herschel) 130-140 km across. Quoting the Wikipedia page on Mimas:
If there were a crater of an equivalent scale on Earth it would be over 4,000 kilometres (2,500 mi) in diameter, wider than Australia.
[The Herschel crater] is so large that astronomers have expressed surprise that Mimas was not shattered by the impact that caused it.
I don't see any estimates on the size of the impact body, but it's probably a safe bet that it was a lot smaller than the resultant crater. If we play nice and say that the impact body was half the size of the resultant crater (it probably was quite a bit smaller than that), that makes the impact body approximately 70 km diameter. What you are proposing is an impact of a body on the order of ten times that size.
This is Mimas, showing Herschel to the Cassini probe (image courtesy NASA, photo ID PIA12570):
An impact on Earth by such an asteroid, under that assumption, would result in a crater a thousand kilometers across. A more reasonable guess is probably a factor of ten times, which means that if the Earth survived, the crater would be on the order of 5000 km across.
The diameter of the Earth is a little less than 13000 km.
Under those assumptions, the crater would represent more than a third of Earth's diameter, quite comparable to Herschel in comparison to Mimas. If the size amplification of the crater compared to the impact body is even larger, the crater caused by a 500 km body impact becomes larger than that. I think it stands to reason that a crater around a third of the diameter of the body it appears on is as large as it can become, based on the fact that to my knowledge, we are not aware of any larger craters anywhere in the solar system.
If the Earth would survive such an impact, I imagine that scientists would be equally surprised as they are about the Herschel crater. (And of course, such an impact would wreak complete havoc with the environment, but you are asking about plate tectonics.) Or said in another way: I doubt the planet would survive the impact, so plate tectonics don't enter into the picture.