I have to admit that my mainframe days are fading into the past, but wasn't there a utility program called IEBCOPY or something that you could use? As I remember, spaces are not valid in mainframe dataset names, but it seems to me that you could use mainframe utilities to rename the file from:
G741270.DATASET.NAME to LATEST.DATA.FILE
Or even better, just use the name you want in your SAS program (if you are using SAS to create G741270.DATASET.NAME ). The only way that I can think of to do it with SAS is to issue an X command that issues a TSO command to do the rename OR an X command to invoke a CLIST, but if you're doing this in batch JCL, then you might need a different approach.
This is probably a question that is best answered by Tech Support, since they are better in tune with how to do things on the mainframe these days.