Below is what you'll find in the manifest.xml

To edit the file, right click on it and go to Open With-->Notepad

If you don't see Notepad, then click on Choose Program... and pick it from the list.

 

Change the numbers around in the red text, but be sure to leave the same number of characters.
ex. 11000000-0000-0000-0000-0000000000A this is an acceptable change, but if you ever come across another expression with the same ID number, one will overwrite the other.

Change the blue text to the title of your expression, make sure they all match

Change the green text, keeping letters as letters, and numbers as numbers. Make sure they are all the same. Just change one and copy and paste it in the other locations.

<?xml version="1.0" encoding="UTF-8"?>
<DOCUMENT EXPIRATION="06/30/2007" PackageType="00" SLEVEL="00" ID="00000000-0000-0000-0000-0000000000A">
<THEME ID="00000000-0000-0000-0000-00000000000A">
<NAME LANG="EN" TEXT="Name Of Theme"/>
<SET ID="AIM-STANDARD" TYPE="SMILEYSET"/>
<SET ID="AIM-STANDARD" TYPE="SoundSet"/>
<SET ID="Name Of Theme" TYPE="DisplaySet"/>
</THEME>
<RESSET TYPE="DISPLAYSET" ID="Name Of Theme">
<NAME LANG="EN" TEXT="Name Of Theme"/>
<RESREC TYPE="Display" ID="BLBKGND"
BART="a0a0a0a0aa0000==" FILE="blbkgnd.bmp"/>
<!-- includes BLFILLCOLOR, BLCONTENTBAR -->
<RESREC TYPE="Display" ID="BUDDYSKIN"
BART="a0a0a0a0aa0000==" FILE="blskin.xml"/>
<RESREC TYPE="Display" ID="IMICON"
BART="a0a0a0a0aa0000==" FILE="icon.gif"/>
<!-- includes IMCONTENT -->
<RESREC TYPE="Display" ID="IMSKIN"
BART="a0a0a0a0aa0000==" FILE="imskin.xml"/>
<RESREC TYPE="Display" ID="IMBKGND"
BART="a0a0a0a0aa0000==" FILE="imbkgnd.gif"/>
<RESREC TYPE="Display" ID="BLIMAGE"
BART="a0a0a0a0aa0000==" FILE="blimage.gif"/>
</RESSET>
</DOCUMENT>