It could if they wanted to be pedantic.
My S3 pictured in my avatar started out life as a troop carrier and from memory was listed in rego as a mini-bus or something like that (this is a few years ago)
You may have problems if you have retrofitted seat belts to your vehicle and so the new mounts would need to be certified, but that is only if transport goes over things with a fine tooth comb.
If you do it get some decent rubber seals, top and bottom for the new cab. Go see the mob near the roundabout at south pine road at enoggera (cant think of their name but they specialise in rubber for restorations).

