Here's a somehwat more detailed howto:
http://www.modthesims2.com/download.php?p=2128586#post2128586This is specifically for the case where both source and target nhoods already have lots in them. If you look further downthreads (around post #150 I believe), a few people have done it along these lines as well.
As for the sims, the most sensible thing to do is indeed moving them out like you did, changing the hood + lots, and then moving them in again.