User exit for GR non-valuated checkbox

HI Experts,

In ME21N and ME51N,when user select Distribution account assignment (Distrib. on quantity basis/ Distribution by percentage), GR non-valuated (In Delivery tab) become checked automatically.

When select back Single account assignment, GR non-valuated will not be un-checked automatically. Do anyone know what user exit can be use to uncheck the GR non-valuated check-box automatically when select single account assignment?

I saw the same question in forum but there is not correct answer. Please help.