Hi...
Using user-exit EXIT_SAPLKEAB_004, you can apply the costing key which you want when you execute KE27.
Refer to my sample coding.
DATA : ITEMKC00 LIKE CE0KC00.
CHECK I_BWFKT = '02'. "Point of valuation : Periodic valuation of actual data
ITEMKC00 = IS_COPA_CHARACTERISTICS.
CASE ITEMKC00-PERIO+4(3) . "PERIOD
WHEN '001'.
ES_OUTPUT_FIELDS-KALAW1 = 'M01'.
WHEN '002'.
ES_OUTPUT_FIELDS-KALAW1 = 'M02'.
WHEN '003'.
ES_OUTPUT_FIELDS-KALAW1 = 'M03'.
WHEN '004'.
ES_OUTPUT_FIELDS-KALAW1 = 'M04'.
WHEN '005'.
ES_OUTPUT_FIELDS-KALAW1 = 'M05'.
WHEN '006'.
ES_OUTPUT_FIELDS-KALAW1 = 'M06'.
WHEN '007'.
ES_OUTPUT_FIELDS-KALAW1 = 'M07'.
WHEN '008'.
ES_OUTPUT_FIELDS-KALAW1 = 'M08'.
WHEN '009'.
ES_OUTPUT_FIELDS-KALAW1 = 'M09'.
WHEN '010'.
ES_OUTPUT_FIELDS-KALAW1 = 'M10'.
WHEN '011'.
ES_OUTPUT_FIELDS-KALAW1 = 'M11'.
WHEN '012'.
ES_OUTPUT_FIELDS-KALAW1 = 'M12'.
ENDCASE.
E_REQUEST_HANDLED = 'X'.