Legal Question in Criminal Law in Michigan

Perjury is a statement made while "under oath" to tell the truth. Your written or verbal statement to police would not have been a statement under oath. You didn't "raise your right hand and say....", with someone "searing you in" like would happen in a courtroom proceeding. If something in your original statement is untrue or needs to be corrected, you should contact the investigating agency and have a new verbal or written statement taken. Obviously, police and prosecutors take action in reliance on the information that is in the original packet of reports, but if that information changes the prosecutor might view the case against the original accused differently. I said "might" because when original witness statements take a 180-degree turn, the circumstances of the changes are also looked at (e.g., was the change due to an honest mistake; was the change due to improper influence, or threats, or collusion). Please note that you may want to consult with your own legal counsel before you contact police because in some circumstances a person can be prosecuted for a crime of "filing a false police report". Without knowing more about your connection to the original case being investigated, what you originally reported, what is now different, and the reasons for the changes, I cannot speculate whether you are at risk. But an attorney reviewing all of that as your legal counsel should be able to advise you on your best plans.

It would not be perjury because it wasn't a statement given under oath. However, depending on what the retraction is it could be grounds to have you charged with filing a false police report. I would advise you to seek legal counsel from an experienced criminal defense attorney before contacting or speaking with the police about what statements you are going to retract and what the consequences might be.