Hi,
I am not sure if I fully understand your remaining issue.
As I suggested you are using one variable of type customer-exit which is input-ready.
In i_step = 1 (before variable pop-up) you can prepare the default value(s) which will be displayed on the variable pop-up. In the coding you have written: C_CHECK_AGAIN to 'X' (necessary to call the customer-exit again in i_step = 2).
On the variable op-up the user can accept or modify the values.
In i_step = 2 (after variable pop-up) the customer-exit is called again. I expect that the values of the variable are available in I_T_VAR_RANGE. You can validate if there are OK, make any modifications if required and finally populate C_T_RANGE.
Please let me know if everything is clear.
Best regards,
Sander