Hi Toidi. 3 ideas:
1. Yes, you can change in your test sys the tech compleate day. Table AUFK-IDAT2, I did lots of times without problems, but doit at your own risk (I mean, im not responsible if you damage something 
).
2. If You just want to settle (not run WIP test) in the previous month, you can set the final indicator to the goods movement 101 of Co-Products. So, post quantity "0" and the check final delivery with a previous month day, so you dont need the TechCompleate to FULL settle your production order.
3> Why you dont do the ML period end Close in April? you only need to change the MM period in MMPV to MAY. If you recive an error message, there is a OSS that allow you to change period in advance *
| 1082841 | MMPV: Prevent shifting to a future period by mistake |
Arturo!