SSC and STC files are text files so you can open them with any text editor. Using the Modify and Replace keywords lets you change or replace things without changing the original files. An example of doing this is:
Code: Select all
Modify "Jupiter" "Sol"
{
NightTexture "jupiternight.png"
}
Create a text file with an editor like Notepad, put the above text in it and save it with a name like Jupiter_mod.ssc in the extras folder. You could put the jupiternight.png file in the textures/medres folder, but if you don't want to fill up that folder with lots of files, you could create new textures/medres folders inside the extras folder to put the jupiternight.png file in.
If you want to keep things organizated, you could make a folder inside the extras folder for each addon. For example, you could make a folder Jupiter_mod in the extras folder and put the SSC file and the SSC file's own texture/medres folders in it. Doing this would make it easy to move addons into and out of the extras folder to control what addons are loaded when Celestia starts up.
I'll also add that I also have addons in the main Celestia folder and listed in the ExtraDirectories section of celestia.cfg with one folder name per line of the list. I commet out the ones I don't need now with # at the start of the line.
For more information about the structure of addons, see:
http://www.lepp.cornell.edu/~seb/celestia/addon-intro.html