I have heard of transpositions happening by default for customers of iiNet Group as well... but I am not sure about specific ISPs and their agreements with TW
To be fair, the Front Of House sale people would likely have no idea what a transposition was at Telstra too... unless you are lucky... however if it does get to a rejection stage, the BOH team who let you know should be able to confirm that it was tested for transposition if it was.
The restriction of speaking to TW was meant to be to remove any untoward behaviour... but any ideas like that come with some drawbacks, like this as an example... the NBN is pretty much the same, just with NBN Co instead of TW as the wholesaler.