adding goldfish to pond in winter?

The question: is it safe to move a 6 inch sarassa comet goldfish from a
very small outdoor pond (50gallon) to a larger 700 gallon pond when...

1-the larger pond is much colder and the fish are already hibernating?
2-the smaller pond fish are active and still feeding?

I live in soCal and the owner of the large fish finally came to the
conclusion that his small pond is way overstocked and the likelihood of this
large and very beautiful fish surviving for much longer in an overstocked
tub are slim.

Thanks for your help.