Can a bnei noach have a mezuzah? And would just having it, not hung up. Be a violation of any laws? I am a noahide and I had already bought a mezuzah that I wasn’t originally planning on buying.

Shalom, Thank you for your question. No, it is not forbidden for a Noahide to own a mezuzah (although it might have been problematic for the Jew to sell or give to the non-Jew). It should be treated with the greatest of respect. As I have written in other responsa, I believe that a non-Jew should not put up a mezuzah on their doorposts. If you ever want to relinquish the mezuzah, please make sure that it gets into the hands of an Orthodox religious Jew, who will know what to do with it. Blessings.