I just read back through all of the posts and I think you're right. The first post does say
I have the 15000 user record's in a DATASET.
I guess all the talk about commands confused me - I thought he was asking how to change fields in an input file, not how to generate commands from an input file.
If the OP had just said in his first post:
I have 15000 user records in a dataset. I want to generate 15000 commands like this:
CHANGE <userid> REGION(rgn)
where userid is at positions a-b in the file and rgn is at positions c-d in the file.
then it all would have made sense.
Is that what you actually want? If so, then give the starting position, length and format of the userid and rgn fields in your input records, give the RECFM and LRECL of the input file and the output file you want to generate, and show an example of the input records and what you expect for output.