Its possible but messy in that, (what I know), the unit that owns the car space will have to cease to exist and a new strata plan submitted which involves survey, registration, possibly council approval fees permission from board and strata Manager and then that unit will get a new lot number without the car space.
However some unit blocks have the unit and car spaces as two separate lots and in this case you can just buy the lot number for the car space.
Hope this helps a bit.
Fleur