First, there is a lot more detail you ought to give us, especially which version of MEP?
However, I do not think there is any way in which you could achieve what seems to be your aim. MEP can open/edit wmv files, but as soon as you attempt to "export" the new video as wmv, I'm pretty certain MEP must re-encode it. Simply "saving" the project does not give you a new video file, you are merely saving the file which tells MEP exactly how you want the finished product to "look".
Like Jeff, I don't really understand your question properly without more infomation. In particular, what are you planning to do with the finished WMV?
If it's now completely finished after the cut, are you going to play it on your PC? If so then why not just put both parts in say a VLC playlist and play part 2 immediately after part 1. Haven't tried it but it might work if the join coincides with a short pause or fade.
If you're continuing with the editing, or even just want to make a DVD from the project at this stage, then obviously you're going to have to render it!
Or maybe you're just frustrated, as I remember I was originally, after making a DVD with one tiny error (it was a typo in my case) and the whole thing has to be re-burnt.
. . . . how to cut a movie without having to re-encode it? . . . .
You can't - and this applies to all the Non Linear Editiing video editors available.
As soon as you make a cut and remove a section of the video you are in effect 'breaking up' the orderly stucture of frames within the video and these have to be reconstructed, ie re-encoded, into an ordely structure again when you want to create the finished product with the section removed.
Movie Edit Pro is a non destructive editor ie it does not make any changes to the original video files, it is only when you want to export or create a DVD that re-encoding takes place.
There are functions in MEP called Smart render and Smart copy where you can export an MPEG or AVCHD file susquent to simple cutting in the timeline, without re encoding every frame (very fast). However as your file is WMV, I believe this is not possible.