MDR article 120 significant changes

Yes, it is, because you need to prove that the new company that provides sterilization is just as good as the previous one (so that it has a valid ISO 13485 certificate for its type of sterilization, that you have sterilization validation results with the new provider, that you have done biological indicator tests with the new provider, etc.). Also, in your risk analysis, you should check whether any new risks have appeared with the change of sterilization provider: for example, how long is the transport from you to the new provider, is it longer or shorter, has the responsibility for transport changed.