WHV -> tourist visa

Hi there!
I was researching and apparently it is possible to change a WHV to a tourist visa w/o leaving the country. However I asked immigration and they said it wasn’t possible. I forgot to ask them, but is it possible to leave before my visa ends, then go to a neighboring country (Korea, etc) for a week and then come back as a tourist? Or would I have to go back to my country before coming back?

I don’t mind going back straight home but there was a test I would like to take that takes place after my visa ends.

Thanks in advance