Another widely-used solution to the problem is known as a bogie exchange: each carriage, wagon or locomotive is put on a section of dual-gauge track under a heavy crane. It is then lifted off its bogies, which are pulled out and replaced by equivalent bogies of a different gauge. This technique was first used on Victorian Railways' diesel locomotive B60, and has been widely used for freight cars, especially in the wheat harvest season when every wagon is badly needed. However it is relatively slow in practical terms, because a train must be broken up and each wagon treated separately.
http://www.kepl.com.au/ihvic/allaboard.html
it was a common problem here in .au for a while lol and they did indeed swap out bogies
not sure exactly how many different gauges ended up in use in australia-3 major(in different states australiawide) and several minor ones
edit to make it clearer the guages were in different states