if it contains no level blocks, only models, sprites, and wmb map entities, then you can use the "save as .wmb" code created by Emre. it can be found within Lite-C contribution topic.

its main feature to export the currently loaded level as a .wmb, but also saves a .$$m file which can be opened by WED. maybe once it will be extended to work with level blocks and prefabs too...

or you can use the SDK.