I have changed resorts in the middle of a stay several time, and have always had Disney move my luggage for me. My most recent experience was moving my luggage from the Polynesian to the Beach Club in August. I had the bellmen pick up my luggage in the morning before heading to the Magic Kingdom, and my luggage was there by the time I checked into the Beach Club at about 2:00. I tipped the bellman who picked up my luggage at the Poly, and the one who brought my luggage to me at the Beach Club. I tipped $1 per bag to each of them.
I would definitely have Disney move my luggage again, and will be doing that in a few weeks when I move from the CBR to the Boardwalk.
Karen