When both plants have same warehouse, and the physical stock also in Same bin, In WM Movement Type, enable Post to Same bin. Then, Do your stock transfer between plants, you will get a posting change document,
If you have automatic TO Creation enabled, You will get a TO with Source and Destination as same bin. With this, you can also do stock transfer during cut over as well.
Let me know, if it resolve your problem.
Regards,
Sathish