Retrieving data without modifying the original called program

REPORT ZSCRIPTPERFORM.
FORM GET_BARCODE TABLES IN_PAR STRUCTURE ITCSY
OUT_PAR STRUCTURE ITCSY.
DATA: PAGNUM LIKE SY-TABIX, "page number
NEXTPAGE LIKE SY-TABIX. "number of next pageREAD TABLE IN_PAR WITH KEY 'PAGE'.

CHECK SY-SUBRC = 0.

PAGNUM = IN_PAR-VALUE.

READ TABLE IN_PAR WITH KEY 'NEXTPAGE'.

CHECK SY-SUBRC = 0.NEXTPAGE = IN_PAR-VALUE.
READ TABLE OUT_PAR WITH KEY 'BARCODE'.
CHECK SY-SUBRC = 0.IF PAGNUM = 1.
OUT_PAR-VALUE = '|'. "First pageELSE.
OUT_PAR-VALUE = '||'. "Next page
ENDIF.
IF NEXTPAGE = 0.
OUT_PAR-VALUE+2 = 'L'. "Flag: last page
ENDIF.
MODIFY OUT_PAR INDEX SY-TABIX.
ENDFORM.