Im remaking my post, im not sure i knew what i wanted to ask…
After reading quite alot it sounds like what im looking for is a "terrain brush". I have tried monkeyworld3d version 3 now and I cant see that theres any
way of painting the terrain with different textures. What I would like to do is just pick a texture and paint with it like a brush on the terrain. For example where theres a road you could just paint the rocky road texture directly on the geometry. Is this coming in monkeyworld3d at a later time? Has someone used this technique before with jmonkeyengine and did you use a utility for it?
This is a feature I'm looking for also. Not sure if MonkeyWorld has this, if it doesn't then this feature is a must.
jMonkeyEngine/MonkeyWorld do not have it right now. However, a system has been released which enables those to use texture painting (the technique which you're looking for); more information is available at the thread: http://www.jmonkeyengine.com/jmeforum/index.php?topic=5598.0
And of course, there's still:
http://www.jmonkeyengine.com/jmeforum/index.php?topic=4146.0
If you don't need shader-free support for older cards or fixed pipeline fog. At the very least it can serve as an example how to update alpha maps, and how to paint on them using mouse ray picking.
MonkeyWorld doesn't have this feature yet, but we are trying to add this in future versions. What we want to have is this: http://www.jmonkeyengine.com/jmeforum/index.php?topic=5641.0
We are constantly trying to bewitch hevee to help us out with this feature 
or you could use a shader free solution with something similar to PassNode…see TestTerrainSplatting and TestIsland for terrainsplatting demos in jme…
Looking at this “feauture” page of the last version of monkeyworld3d it looks like this is what i need,
texture splatting but its strange, I dont understand why people say its not supported.
Look here at the texture section right under the water-picture… and the version showing texturesplatting is 2.09 
It certainly looks like theyr painting a texture on the ground in that screenshot…theres even a red circle thats probably shows where to paint etc… Or am I wrong?
http://monkeyworld3d.sourceforge.net/mw3d3-milston-nn.html