MSI: when upgrading, delete a file that is implicitly the KeyPath of the component

I have an MSI (built with Wix 3) already distributed to customers. Among others, the product has a directory named Reporter that contains two files, A and B. A is the implicit KeyPath, because it is the first entry in the XML.

For security reasons, we need to eliminate file A. So we need to produce an MSI that:

• does not contain A
• on upgrade, removes A, but keeps file B (in the same component, in the same directory)
• on clean install, deploys only B (obviously)

Here is the current WXS file:

<Directory Id="DirX" Name="Reporter">
    <Component Id="componentX" Guid="47A2D991-AC4D-43C0-94F3-02E3D4D2AB3D" DiskId="1" Win64="yes">
        <File Id='A' Name='A' Source='A'/>
        <File Id='B' Name='B' Source='B'/>
    </Component>
</Directory>

<Feature Id="featureX" Title="bla" Level="1">
    <ComponentRef Id="componentX" />
</Feature>

How can one reasonably accomplish this? Remarks:

• no we cannot keep file A

• it would be very nice to keep file B in the same directory (Reporter)

• we usually perform minor upgrades

• we don't really care about features or components, the product is usually installed as a whole by network admins, without user interference.

I tried everything I could find on the internet:

• setting file B as KeyPath -> on upgrade, the entire directory Reporter is wiped.
• creating a new feature, new component, new GUID, with only file B -> on upgrade, the entire directory Reporter is wiped.
• using RemoveFile for file A -> same result

I am reluctant to create a custom action, but will do if that is the only way.