@desertrunner… can you please post your solution?
I would, if I had one. 
I'm still working on it. But at the moment I'm concentrating on GUI parts. Maybe I can post my solution in a few days.
i have solved it now by myself
i added following functions to TerrainBlock.java
/**
* <code>setHeight</code> sets the height of an arbitrary point on the
* terrain.
*
* @param x
* the x coordinate to check.
* @param z
* the z coordinate to check.
* @param height
* the new height
* @return the height at the provided location.
*/
public void setHeight(float x, float z, int height) {
x /= stepScale.x;
z /= stepScale.z;
float col = FastMath.floor(x);
float row = FastMath.floor(z);
if (col < 0 || row < 0 || col >= size - 1 || row >= size - 1) {
return;
}
// calculate hight map point
int focalSpot = (int) (col + row * size);
// set heightmap point
heightMap[focalSpot] = height;
}
and the following to TerrainPage.java
/**
* <code>setHeight</code> sets the height of an arbitrary point on the
* terrain.
*
* @param x
* the x coordinate to check.
* @param z
* the z coordinate to check.
* @param height
* the new height
*/
public void setHeight(float x, float z, int height) {
// determine which quadrant this is in.
Spatial child = null;
int split = (getSize() - 1) >> 1;
float halfmapx = split * getStepScale().x, halfmapz = split
* getStepScale().z;
float newX = 0, newZ = 0;
if (x == 0)
x += .001f;
if (z == 0)
z += .001f;
if (x > 0) {
if (z > 0) {
// upper right
child = getChild(3);
newX = x;
newZ = z;
} else {
// lower right
child = getChild(2);
newX = x;
newZ = z + halfmapz;
}
} else {
if (z > 0) {
// upper left
child = getChild(1);
newX = x + halfmapx;
newZ = z;
} else {
// lower left...
child = getChild(0);
if (x == 0)
x -= .1f;
if (z == 0)
z -= .1f;
newX = x + halfmapx;
newZ = z + halfmapz;
}
}
if ((child.getType() & SceneElement.TERRAIN_BLOCK) != 0)
((TerrainBlock) child).setHeight(newX,newZ,
height);
else if ((child.getType() & SceneElement.TERRAIN_PAGE) != 0)
((TerrainPage) child).setHeight(x
- ((TerrainPage) child).getLocalTranslation().x, z
- ((TerrainPage) child).getLocalTranslation().z, height);
}
/**
* <code>setHeightFromWorld</code> sets the height of an arbitrary point
* on the terrain when given world coordinates.
*
* @param height
* new height
* @param position
* the vector representing the height location to check.
*/
public void setHeightFromWorld(int height, Vector3f position) {
Vector3f calcVec1 = new Vector3f();
Vector3f locationPos = calcVec1.set(position).subtractLocal(
localTranslation).divideLocal(getStepScale());
locationPos.multLocal(getStepScale());
setHeight(locationPos.x, locationPos.z, height);
}
the code to find the points is copied from the getheight functions.