Need help with the abap code for Bex field display

The 'Rate' field in a Bex Query is showing all the values as $ (Amount). This field is KONV-KEBTR in ECC and can have a value as $ or %. The logic will be in KONV table, if the field KONV-KRECH(calculate.type) NOT equal to "A", then show $Amount and if KONV-KRECH = "A", then it should show %. Also, when the field KONV-KEBTR is %, the value should be value/10 (divided by 10).

Please advice where is the best place to code - source system extractor or a customer exit in Bex?

Thanks,

Dilip