SWR might not agree for 3 issues:
1) If extended to MYS, SWR might have to workout on the slack time b/n SBC-MYS. In that case, the duration might be fixed for 3 hrs to compensate the slack. It will lose the SF tag in that case.
2) There is a long pending request to send it to Chennai to free up the PF at SBC. That RSA plan might be hampered if this is extended to MYS.
3)...
more... Morning path for MYS from SBC is too busy. SWR might find it tough to get the slot even if one train runs late.