Is it permissible to remain in a job that involves changing the expiry dates of ink and selling counterfeit products, knowing that this is unlawful, and does the ruling differ if I refuse to participate in these practices or if I am asked to carry them out?

What your colleague is doing—changing the production date and selling inks as if they were produced by another company—is a forbidden deception. You must forbid him from it and not participate in it, even if he asks you to. If you can remain in the job without participating in the deception, while also forbidding the wrongdoing, then there is no harm. However, if you cannot remain except by participating, then it is not permissible for you to do so, except in cases of extreme necessity where you cannot find any other livelihood. "And whoever fears Allah, He will make for him a way out and will provide for him from where he does not expect."