The UV wrapped data is lost. You can add a new material by putting your seamless custom texture in the Textures Folders then start AssetForge. Under Materials, click new material, highlight the texture, hit the Texture tab and browse to your custom texture and choose it.
This works good for walls, floors, wooden furniture and so forth. You can change the scale of the texture under the Materials-Scale Tab.
It will not work with "atlas" texture type single textured objects that rely on the UV wrapping data.
I really like this tool because for certain things and scenes that rely on seamless textures, you can get pretty detailed. It is similar to the way Sketchup handles textures.
Here is very low poly example.