FROM WHERE I CAN CHANGE THE STATUS OF MESSAGE MM016.
I think so many documents, stocks are there in that period, thats might be the reason the system is not allowing to intitialize the period.
You need to write to the SAP to check this Period initialize.They will suggest some solutions for this what needs to be done.
One more thing is I am not sure whether it will work or not.
If the Plant is your Valuation area,
You just remove the assignment of the Plant from the company code in Enterprise structure IMG settings for assignment temporarily.
Then in Transaction OMSY --Maintain the company code for Materials Management you Initialize the period as per your requirement then again assign the Plant to the company code.
Check all your data again, whether the system works or not.
This is suggestion, Please Don't test in Real scenario, Create a dummy company code & Plant and post some documents & Stocks and then try to do follow the above settings then initialize this. Check out will it works or not.