Passing command line args to MSI from WiX bundle - wix

Question

I’m on Wix 3.7. I have an MSI that I would like to set a registry key (perhaps via a Custom Action, as he will have to check if the key already exists).
I understand that a Bundle in a bootstrapper project can't change the machine state (such as setting the registry). Therefore, I'm attempting to pass a command line argument via <MsiProperty>, but doesn't appear to show up as a command line argument in my log file for the bootstrapper.
Is it possible to set a registry key up in a Bundle?
If not, how can I add a command line argument (or some other piece of custom data)
to be passed to the MSI.
How can the MSI read whatever it is I pass to it (whether It ends up being a command line arg or something
else).
Bundle:
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Bundle
Name="MyInstallerBootstrapperLocalDb"
Version="1.0.0.0"
Manufacturer="some company"
UpgradeCode="PUT-GUID-HERE">
<BootstrapperApplicationRef Id="WixStandardBootstrapperApplication.RtfLicense" />
<Chain>
<MsiPackage Id="MyInstallerInstaller"
SourceFile="$(var.MyInstallerInstaller.TargetPath)"
Compressed="no">
<!-- TODO - if this is being set correctly, the MSI needs to
interpret it and set up the key-->
<MsiProperty Name="SetLocalDb" Value="yes"/>
</MsiPackage>
</Chain>
</Bundle>
</Wix>

Answer 1

Your MSI needs to define a property like so:
<Property Id="SOMEPROPERTY" Value="Default"/>
You can then set this property from the bundle:
<MsiPackage SourceFile="<package>.msi" Id="SomeId">
<MsiProperty Name="SOMEPROPERTY" Value="[SomeProperty]" />
</MsiPackage>
After this you can set the property in the Bootstrapper as described here: WiX Bootstrapper: How do I set burn variables from the command line?
Notice that SomeProperty is a Burn variable which you have to define:
<Variable Name="SomeProperty" Type="string" Value="DefaultValue" />
Update:
In the MSI you are then able to do a registry search based on this property:
<RegistrySearch Id="GetSomeValue" Root="HKLM" Key="SOFTWARE\<Manufacturer>\[SOMEPROPERTY]" Name="<ValueName>" Type="raw" />

Answer 2

Just to add an extra bit of information. To alter the variable values with command line, I actually had to set it as overriable.
<Variable Name="SomeProperty" Type="string" Value="true" bal:Overridable="yes" />