Change characteristics in Planning function exit

I am using a planning function EXIT for my planning cube. I have some info objects like unit/ material which are my dimensions/characteristics in my cube.

In my planning function, I am overwriting contents/ assigning values to these info objects [dimensions/characteristics] using class method program.

I am using field symbols to access this hashed table.

But it is giving run time error as "MOVE_TO_LIT_NOTALLOWED_NODATA" Error at assignment: Overwritten protected field. For key figures, it is behaving OK.

Is there any alternate solution for this?