[Windows Phone 8 Development and Hacking] snickler:
Unfortunately, I've tried all of those. I still can't write to the places I want to write :/. It's as GoodDayToDie said, we're pretty much running with no access to change that key. I've been testing with RegistryRT, Nokia.SilentInstaller,Runtime, NrsRuntime and DwrEngine's Registry implementations.

I DID happen to find something VERY interesting unrelated to Registry.. In the extras+info xap, there's functionality to install xaps. Within the xap, there's a "xaps" folder that contains files with .TA1 (.xap),.TA2(.provxml),.TA3(license) extensions. The code copies these xaps to the OEM Shared Folder and proceeds to Install them.

private bool CopyStorageCleanerInstallationFiles()
{
bool result = false;
if (!Directory.Exists("C:\\Data\\SharedData\\Oem\\Public\\emmccleaner"))
{
InstallUtils.LogResult("EMCC cleaner service not installed", LogType.Info, false);
return false;
}
if (!this._storageCleanerInstallManager.ShouldStartWork())
{
InstallUtils.LogResult("Storage cleaner Application is already installed", LogType.Info, false);
return false;
}
string embeddedXapPath = "\\xaps";
return this.CopyInstallationFile(result, embeddedXapPath, "C:\\\\Data\\\\SharedData\\\\Oem\\\\Public\\\\Nokia\\EmbeddedApps\\StorageChecker");
}
private bool CopySpamFilterInstallationFiles()
{
bool result = false;
string regSZValue = InstallUtils.SiRuntime.GetRegSZValue("Software\\OEM\\PhoneSmsFilter", "AppId");
if (string.IsNullOrEmpty(regSZValue))
{
return false;
}
int num = 0;
try
{
Version version = Environment.get_OSVersion().get_Version();
num = version.get_Build();
}
catch (Exception)
{
}
if (num <= 10327)
{
InstallUtils.LogResult("Spam fiter works with build higher than 10327 only", LogType.Info, false);
return false;
}
if (!this._spamFilterInstallManager.ShouldStartWork())
{
InstallUtils.LogResult("SpamFilter Application is already installed", LogType.Info, false);
return false;
}
string embeddedXapPath = "\\xaps\\SpamFilter";
result = this.CopyInstallationFile(result, embeddedXapPath, "C:\\\\Data\\\\SharedData\\\\Oem\\\\Public\\\\Nokia\\EmbeddedApps\\SpamFilter");
return result;
}
private bool CopyInstallationFile(bool result, string embeddedXapPath, string installCache)
{
StorageFolder installedLocation = Package.get_Current().get_InstalledLocation();
if (installedLocation != null)
{
string text = installedLocation.get_Path() + embeddedXapPath;
if (Directory.Exists(text))
{
InstallUtils.LogResult(text + " exists", LogType.Info, false);
try
{
string[] files = Directory.GetFiles(text, "*.*");
if (files.Length > 0)
{
bool flag = Directory.Exists(installCache);
if (!flag)
{
DirectoryInfo directoryInfo = Directory.CreateDirectory(installCache);
if (directoryInfo.get_Exists())
{
flag = true;
}
}
if (flag)
{
if (files.Length == 0)
{
result = false;
}
string[] array = files;
int i = 0;
while (i < array.Length)
{
string text2 = array[i];
string text3 = text2;
string text4 = Path.GetFileNameWithoutExtension(text3);
string extension = Path.GetExtension(text3);
if (string.Equals(".ta1", extension))
{
text4 += ".xap";
goto IL_112;
}
if (string.Equals(".ta2", extension))
{
text4 += ".xml";
goto IL_112;
}
if (string.Equals(".ta3", extension))
{
text4 += ".provxml";
goto IL_112;
}
InstallUtils.LogResult("Unknown file found , file name is " + text3, LogType.Info, false);
IL_169:
i++;
continue;
IL_112:
string text5 = Path.Combine(installCache, text4);
if (!File.Exists(text5))
{
result = this.CopyFile(text3, text5);
InstallUtils.LogResult(string.Format("Copying {0}\t to \t{1} \t result is " + result, text3, text5), LogType.Info, false);
goto IL_169;
}
InstallUtils.LogResult("File already exist, no need to copy to " + text5, LogType.Info, false);
result = true;
goto IL_169;
}
}
}
return result;
}
catch (Exception ex)
{
InstallUtils.LogResult(ex.ToString(), LogType.Info, false);
return result;
}
}
InstallUtils.LogResult(text + " not exists", LogType.Info, false);
result = false;
}
return result;
}
}

private void TriggerInstall(uint minParallelInstallCount = 1u)
{
lock (this._installationQueue)
{
int num = 0;
while ((long)num < (long)((ulong)minParallelInstallCount))
{
if (this._installationQueue != null && this._installationQueue.get_Count() > 0)
{
InstallUtils.FreeMemory();
PreloadApplicationInfo preloadApplicationInfo = this._installationQueue.Dequeue();
if (preloadApplicationInfo != null)
{
InstallUtils.LogResult(string.Format("TriggerInstall, Dequeue'd the top application and triggering install SourceLocation is {0}", preloadApplicationInfo.SourceLocation), LogType.Info, false);
this.CreateRegistryDataForPreloadedApp(preloadApplicationInfo);
preloadApplicationInfo.Install();
}
}
else
{
InstallUtils.LogResult("Application installation queue is empty", LogType.Info, false);
}
num++;
}
}
}

private void ApplyAppInstall()
{
try
{
this.InstallState = 1;
this.InstallStartTime = DateTime.get_Now().ToString("hh:mm:ss.fff tt");
IAsyncOperationWithProgress<PackageInstallResult, uint> op = InstallationManager.AddPackageAsync(this.Title, this.SourceLocationUri, this.InstanceId, this.OfferId, this.LicenseUri);
op.put_Completed(delegate(IAsyncOperationWithProgress<PackageInstallResult, uint> info, AsyncStatus status)
{
switch (status)
{
case 0:
InstallUtils.LogResult("AddPackageAsync() reported AsyncStatus.Started for " + this.Name, LogType.Info, false);
return;
case 1:
{
PackageInstallResult results = op.GetResults();
this.InstallEndTime = DateTime.get_Now().ToString("hh:mm:ss.fff tt");
this.InstallState = results.get_InstallState();
return;
}
case 2:
InstallUtils.LogResult("AddPackageAsync() reported AsyncStatus.Canceled for " + this.Name, LogType.Info, false);
this.InstallEndTime = DateTime.get_Now().ToString("hh:mm:ss.fff tt");
this.InstallState = 0;
return;
case 3:
this.InstallEndTime = DateTime.get_Now().ToString("hh:mm:ss.fff tt");
if (op.get_ErrorCode() != null)
{
InstallUtils.LogResult(this.HandleException(string.Format("AddPackageAsync() reported AsyncStatus.Error -> Error occured when installing\t{0}", this.Name), op.get_ErrorCode()), LogType.Info, false);
this.ErrorCode = op.get_ErrorCode();
return;
}
InstallUtils.LogResult(string.Format("AddPackageAsync() reported AsyncStatus.Error -> Error occured when installing\t{0}\tErrorCode is null and Progress is {1}", this.Name, this.Progress), LogType.Info, false);
this.InstallState = ((this.Progress == 100u) ? 2 : 0);
return;
default:
return;
}
});
op.put_Progress(delegate(IAsyncOperationWithProgress<PackageInstallResult, uint> info, uint progress)
{
this.Progress = progress;
this.NotifyProgress();
});
}
catch (Exception ex)
{
string log = this.HandleException(string.Format("AddPackageAsync() exception caught-> Error occured when installing\t{0}", this.Name), ex);
InstallUtils.LogResult(log, LogType.Info, false);
this.InstallEndTime = DateTime.get_Now().ToString("hh:mm:ss.fff tt");
this.ErrorCode = ex;
}
}