Customer Exit for Formula Variable

Question

Hi all, and thanks in advance for your help on this one.
I'm trying to run a function module to convert the value of a characteristic in my ODS to a formula variable. To do this, I've created a replacement path variable to hold the value of the characteristic, and then I'm passing this value to another module to convert it to factory date.
Here is my code ZTSTGIDT is the name of the replacement path variable that is set to equal the characteristic key value.
DATA: CONVERTDATE  TYPE SYDATUM. " Date
DATA: FAC_DATE     TYPE FACDATE. " Factory Date
DATA: ZE_T_RANGE TYPE RSR_T_RANGESID WITH HEADER LINE.
    WHEN 'ZFACDY01'.
        CLEAR: ZE_T_RANGE, E_T_RANGE.
*  Get the Goods Issue date from the formula variable.
    IF I_STEP = 2.
      READ TABLE I_T_VAR_RANGE
      WITH KEY VNAM = 'ZTSTGIDT'
      INTO CONVERTDATE.
      CALL FUNCTION 'DATE_CONVERT_TO_FACTORYDATE'
      EXPORTING
      CORRECT_OPTION = '+'
      DATE = CONVERTDATE
      FACTORY_CALENDAR_ID = 'ZB'
      IMPORTING
      FACTORYDATE = FAC_DATE
      EXCEPTIONS
      CALENDAR_BUFFER_NOT_LOADABLE = 1
      CORRECT_OPTION_INVALID = 2
      DATE_AFTER_RANGE = 3
      DATE_BEFORE_RANGE = 4
      DATE_INVALID = 5
      FACTORY_CALENDAR_NOT_FOUND = 6
      OTHERS = 7.
      IF SY-SUBRC = 0.
          ZE_T_RANGE-LOW = FAC_DATE.
          ZE_T_RANGE-SIGN = 'I'.
          ZE_T_RANGE-OPT = 'EQ'.
          APPEND ZE_T_RANGE to E_T_RANGE.
      ENDIF.
    ENDIF.
The variable ZFACDY01 does not receive a value from this code, and it seems as if the variable CONVERTDATE never receives a value from the replacement path variable.
1.) Is it even possible to read the characteristic value in this way?
2.) Is there another way to read the characteristic value directly from my ODS at runtime for the record in question?
The much easier solution is to create new key figures for each date that we need to convert to factory days and to do the conversion in the update rules, but doing so would require extensive reloads of many years worth of data. Even though performance will be impacted, we're trying to find a workaround (queries will be batch-run at night, anyway).
Many thanks (and points!) for the person who can figure this out

Answer 1

I tried using different I_STEP stages, but the replacement path variable still doesn't seem to be populated when it passes the value to the function module to convert to factory days.