https://sma.nasa.gov/sma-disciplines/planetary-protection
https://www.esa.int/Science_Exploration/Human_and_Robotic_Ex...
There's a handbook and everything:
https://ec.europa.eu/research/participants/documents/downloa...
Then again, there's plenty of theories that asteroids and other impacts have caused enough of a splash to throw trace life bearing materials into space and eventually onto other planets or moons.
My current theory is that we will find traces of e.g. bacteria all over our solar system, but it'll be genetically traceable back to Earth. That said, if it turns out life as we know actually started on e.g. Mars, that would be huge and probably a big accelerator for more missions there.
Mining ice deposits would be a pretty hairy business, as any surviving microorganisms would be compatible with our biology.
And obviously absence of anything toxic. In short lot of things need to align.
Now, even if there are conditions favorable for our bacteria, the question of competition remains. Hypothetically, the invaders can carve niche in local ecology, as they often do on Earth, or they might utterly fail, as happens even more often on Earth.
If there are organisms on Europa already, and that is a big 'if', they would have several billions of years worth of head start adapting to the environment and molding it to their image. Conversely, newly introduced bacteria, already damaged by exposure to deep space and deprived of nutrients for many months or years, would see it for the first time.
It isn't given that this experience would work out for them, to say at least.