pass values to the sysin control card through rexx
You need to provide more details. Where is the rexx running? What does your JCL look like.
It could be as simple as two job steps... the first is a rexx program that builds the SYSIN using a:
//FILE1 DD DISP=(NEW,PASS),DSN=&&TMP
The second step would refer to the file with
//SYSIN DD DISP=(OLD,DELETE),DSN=&&TMP