There was one incident in the newspaper where a Geelong train was routed via Broadmeadows and then via Sunshine and Newport which made it very late.
There are a couple of times when both Overlands were routed via Mt Gambier and an Adelaide/Melbourne Express routed via the Balmoral line. In the days before bustitution.
I'm trying to recall other re-routings.
I have a luggage story, in the '70s there were two DERMs to Echuca, one via Bendigo and one via Toolamba/Kyabram. A lady on the ex Bendigo DERM became frantic when her luggage wasn't on it. It turned out if you don't say anything when sending the luggage, the staff will put it on the earliest train. In this case her luggage went via Toolamba while she went via Bendigo and arrived in Echuca ten minutes before she did.
Regarding the Melbourne/Sydney expresses going via Robertson, I have recalled a Spirit of Progress running via Cowra, may have happened more than once. Usually due to a derailment.