Originally Posted by henry999
Are you sure about this? As long as it's the same route, such a carrier change might be the same as a simple date change -- i.e., rebooking rather than reissue.
Henry
There is another theread
here , discussing this issue. Looked like changing from SQ to TG meant it was a re-issue. This was e-tix though. With paper ticket, it should be possible to do without a re-issue.
OTOH, to the OP, If you do have to re-issue, Why not go HKG-BKK-BOM (TG), or HKG-ICN-BOM (OZ). but this definitely means a ticket re-issue and re-routing.