Sort JCL - to replace 1st 2 characters

JCL to replace 1st 2 characters of all the records with 'YY'
//STEP010 EXEC PGM=SORT
//SYSOUT DD SYSOUT=*
//SORTIN DD DISP=SHR,DSN=Input file
//SORTOUT DD DISP=OLD,DSN=Output file
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
SORT FIELDS=COPY
OUTREC FIELDS=(1:C'YY',3:3,319)

Note: LRECL of Input file is 321.