Edit multiple Landscapes (Streaming Proxy?)

I created a big map in WorldMachine and exported it in smaller tiles. First I created their maps individually, and imported the heightmap to a landscape. But then comes the problem with syncing up the edges of each landscape if you want to edit them. Is that possible in any way?

Also, I looked into using the Import Tiled Landscapes as a solution. Is there any way to to reapply heightmaps to the Landscape Streaming Proxies(LSP), if edited, after it is created? Or would I need to re-import them all again?
Is there any way to export a LSP to fbx as you can with a normal Landscape?