Hello Alex,
ABC Indicator for cycle count field ABCIN is in table MARC. This is at Article/site level. So you can find an existing field status group applicable for FASH at Logistice/DC or Logistics/store level and add field MARC-ABCIN to that group using OMSR. Then you can make it optional by selecting radio button for FASH using OMS9.
Thanks,
Venu