Now in the GUI version only, you can export your Shelfari data to an XML file and modify it yourself (or build it from scratch).
Once dumped to file, you can choose to use the XML instead of downloading from Shelfari.

Example of a 2 terms dumped to XML: 

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfTerm xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Term>
    <type>character</type>
    <name>Arya Stark</name>
    <desc>\"Princess Arya\" - \"Arya Underfoot\" - \"Arya Horseface\" - \"Arry\" - \"Weasel\" - \"Nan\" - \"Squab\" - \"Salty\" - 10 years old; Youngest daughter of Eddard Stark and Catelyn Tully; Looks like her father and has brown hair and grey eyes; Is missing and presumed dead; Recently caught a ship sailing for Braavos; Meanwhile an impostor Arya has been betrothed to Ramsay Snow</desc>
    <src>shelfari</src>
    <url>http://www.shelfari.com/characters/Arya-Stark</url>
    <matchCase>true</matchCase>
  </Term>
  
  <Term>
    <type>character</type>
    <name>Sansa Stark</name>
    <desc>\"Princess Sansa\" - \"Alayne Stone\" - 13 years old; Eldest daughter of Eddard Stark and Catelyn Tully; Has thick autumn auburn hair and deep Tully blue eyes; Has dyed her hair a burnt brown color so that she is not easily recognized; Was forced to marry Tyrion Lannister but the marriage was never consummated; Sansa is now hiding in the Vale as Alayne Stone, Petyr Baelish's bastard daughter.</desc>
    <src>shelfari</src>
    <url>http://www.shelfari.com/characters/Sansa-Stark</url>
    <matchCase>true</matchCase>
  </Term>
</ArrayOfTerm>

Explanation of different elements:
type:      Can be either character or topic. People should obviously character, anything else should be a topic. Your Kindle may not load the X-Ray if you put something other than those 2.
name:      Self-explanatory.
desc:      The description you want to show for the term. Notice that quotation marks should be escaped with a backslash or your X-Ray will probably fail to load. 
src:       Can be either wikipedia or shelfari. If it is not one of the 2, your description will not show in the X-Ray for that character.
url:       Usually the Wikipedia or Shelfari link that points to either the term itself or the generic URL to the book.
matchCase: Can be true or false. Indicates whether the search should be case-sensitive. Characters and proper names are usually case-sensitive, while items or other glossary terms are not.