No, this is no problem. We can even return samples from comets and asteroids to Earth. Osiris Rex will do just that for asteroid Bennu which is thought to contain organics and have evidence of the origins of life in our solar system, and it’s a body with a remote chance of having dormant life on it, enough of a possibility that they needed to do a planetary protection assessment for it.

The reason that’s okay is because of Greenberg’s “natural contamination standard”

As long as the probability of people infecting other planets with terrestrial microbes is substantially smaller than the probability that such contamination happens naturally, exploration activities would, in our view, be doing no harm. We call this concept the natural contamination standard.

Infecting Other World, American Scientist, July 2001

We get debris from comets and asteroids hitting Earth every year. This doesn’t show that these objects are lifeless or that there is no possibility of hazards from comets or asteroids. But if there is, we are clearly adapted to be able to cope with it. Also though much of the debris does burn up in the atmosphere - a lot of it also survives. Indeed only the outside of large rocks melts - the interior stays cold, the coldness of space and meteorites are often cold to the touch when picked up immediately after they fall. As well as larger meteorites we get numerous smaller ones that mainly burn up in the atmosphere but some debris survives to ground level. If you put out a pan of water for a few days or a week or so in a place where you get not too much by way of other dust, and preferrably reasonably dry - hen sift through the dust that accumulates in it, you’ll find some particles of meteoritic iron amongst it all which you can pick out with a magnet. Similarly there must be many particles that originate from asteroids and comets.

This same argument doesn’t work for Mars though. The problem there is that though there is some material transferred from Mars to Earth - first it happens only every one or two million years that anything hits Mars with enough of an impact to send material all the way to Earth. It takes at least a century to get here, and typically hundreds of thousands, up to 20 million years. You only get a sample of the region that gets hit and most Mars meteorites come from the higher highland regions of Mars, least likely to have life in them. Many of the proposed habitats on Mars are fragile, in surface layers of salt or dust or ice, while the debris sent into orbit from a spreading crater typically comes from some meters below the surface. And life adapted to live in the Mars briny salts or to use even its very thin atmosphere may well not survive the transit through the vacuum of space either.

So, that’s true of any sample you bring back that is isolated from Earth in some way. That would include samples from the geysers of Enceladus, or of Europa if it has them, also from Ceres, because though it gets impacts from time to time, it would take a long time for the material to reach Earth and the situation is rather similar to Mars.

But for asteroids and comets - especially ones that do close flybys of Earth, then we don’t need to worry because they get hit by other tiny asteroids regularly and some material from them has surely hit Earth already. So that’s the clearest case of the natural contamination standard. Other asteroids and comets, if they are of a type that does close flybys of Earth or collides with it, again wouldn’t be a concern, for the same reason, you are just doing something that happens frequently by natural methods anyway.

Comet 67p is not on a collision course with Earth anyway at present, closest to Sun is 1.3 au, but its orbit has been changed several times through close encounters with Jupiter, so there’s the possibility it could turn into an orbit with a close approach or collision with Earth.

If however it’s something that only happens every few million years, say, that’s not enough to say that it is safe for the requirements of planetary protection. We have many unexplained extinctions in the geological record, and it’s not possible therefore to say for sure that some event that happens only every few million years is safe for humanity (it probably is, but you can’t take even a tiny risk with a billion lives).

See also Planetary protection (wikipedia)