Well, thanks for trying to help. But it doesn't work.
When I open another design the 3d models are automatically read from the reuse location so it's no use.
I tried starting Layout, changing the reuse location and then I created an board with that component on it.
I assigned the new model, changed the reuse location in the options to the shared one and saved. It appeared to work for a moment but then guess what, the old model came back.
Any other ideas?