I think Gold Experience's power is the act of transformation itself, instead of forcing something to stay transformed. If it works that way, then Gold Experience's ability just imbues an object with life, transforming it into a plant, or creature, or body part, and that's it. Once it's transformed, the thing stays that way on its own, unless Giorno reverts the transformation.
You know, like pressing Caps Lock instead of holding Shift to type in all caps.
That's why Giorno can't control the creatures he makes and has to hope they act on their instincts in a way that works out for him.
Of course, all of the above is speculation, I'm just trying to think of how it might work.