For terrain deforming there is a script from Widi.
Link:
http://www.opserver.de/coni_users/web_users/pirvu/au/demo/zips/terraindeformer.zipTerrain painting on the other hand is afaik only possible using a shader. I would look for an multitexture terrain shader which uses colormaps. Maybe you can change the colormaps in realtime?
Just a suggestion.
Greetings
