Does anyone know how can I modify the startup.tgd so that TG2 starts with the settings I want in new scene?
You dont have to :)
Create a scene exactly the way you want your start up to be, camera, presets etc and save it somewhere easy to find, call it my_default_settings.tgd if you like (but you don't have to.) Then go to:Edit>Settings>Project Creation>Load from file> Choose file and now navigate to my_default_settings.tgd, select it and click on OK, your done. Next time you open Terragen it will start up with your default settings file.
:)
Richard
oh awesome.....thanks Richard! :)