How can I create a new Windows registry key or modify the value of an existing one?
You can create a new registry key or modify the value of an existing registry key using a <registrySet> action. You will have to include a section like the one below inside an action list section of your XML installer project file.
<registrySet>
<key>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment</key>
<name>MY_APPDIR</name>
<value>${installdir}</value>
</registrySet>