Hi Robotica, thanks for trying to customize Lunascape. You might be able to find search URL information from the website of the search engine you'd like to use. If not, this method might work.
1. Go to the search engine you want to add as a search engine option and do a search. (let's search a word "luna" as an example)
2. Copy and paste the URL of the search results page into the URL field. For example, if that's google, you will see
http://www.google.com/search?q=luna3. Replace the search term (luna) in the URL with %s. So, it will be
http://www.google.com/search?q=%s
If this doesn't work, let us know which search engine you'd like to add.