Question

My installer has to append a value to an existing multistring registry key (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA\Notification Packages):

<RegistryKey Id='RegistryEntry' Root='HKLM' Key='SYSTEM\CurrentControlSet\Control\Lsa' Action="createAndRemoveOnUninstall">
    <RegistryValue Type='multiString' Name='Notification Packages' Value='p1' Action='append'/>
</RegistryKey>

Problem is that, when uninstalling, it is removing the whole key : HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA ie. all values under LSA are deleted, is there any way that i can just delete the value i appended (only p1) and retain the existing values?

Answer 1

The documentation for WiX’s <RegistryKey> element says (emphasis mine):

createAndRemoveOnUninstall

Creates the key, if absent, when the parent component is installed
then remove the key with all its values and subkeys when the parent
component is uninstalled. Note that this value is useful only if your
program creates additional values or subkeys under this key and you
want an uninstall to remove them. MSI already removes all values and
subkeys that it creates, so this option just adds additional overhead
to uninstall.

Additional evidence suggests that the behavior described above applies to multi-string values: the installer engine will automatically remove the appended values on uninstall, preserving the values that were present before the installation.

Therefore, using create instead of createAndRemoveOnUninstall should do what you want:

<RegistryKey Id="RegistryEntry" Root="HKLM"
             Key="SYSTEM\CurrentControlSet\Control\Lsa"
             Action="create">
    <RegistryValue Type="multiString" Name="Notification Packages"
                   Value="p1" Action="append" />
</RegistryKey>