How to update IsAllocated checkbox under Sales Order Line Details from Custom Production receipt screen release?

Hi,

In My ISV Product,

I need to update Allocation check box in Sales Order from Material receipt release.

(Inventory QtyAvail < 0)

I wrote code to update IsAllocated=true for Existing SOLineSplit.
 

After Material Receipt release getting Base SO code Exception that “Qty will go Negative”..So that I am unable to update Allocation in Sales Order.

Error is populating at g.Save.Press() from the Below Image
 

Is there alternate code to update Allocation.