Are you wanting to take the alex rims off the new wheels and replace them with weinmanns? Somebody will have to rebuild the wheels. It'll probably cost you about as much to rebuild your wheels with different rims as to just buy another set of wheels. Just buy another set, or have another set of wheels built with all better parts. This way you can upgrade the hubs and spokes, too. Sell the old ones on eBay.
Here is an example of a website where you can "build" your own wheels by selecting all the components you prefer. Excel builds good stuff - I have a set of fixed gear wheels of theirs.
http://www.excelsports.com/wheel.asp