when would a model become my own?

I have a model of a train paid for.

I have taken said model and chopped it up.into about 8 sections. removed parts of the body. copied other parts and added them. changed the scale of others.

so how much do I have to change to make it my own to do with as I wish,

with out sued?

or would I have to start all over. even if I liked the shape so much that if I did start over it looked like the first one after I had finished chopping?