In previous post, I described how you can add code to your VSTO/COM add-in to disable your Web Add-in loaded from maniferst via the Office Portal:
Removing Web Add-in Ribbon Customization in Outlook for Windows (theofficecontext.com)
Well with Outlook for Windows, Office 365, version 16.0.13728.36136, you can now disable your Web Add-in via Policy settings.
Here is the path in the policy editor for this setting:

Once in the policy editor, you would set the value. If your OfficeJS Web Add-in has a GUID of {c5bc7737-0d79-4302-9e73-2a614941e914} and the COM add-in is called “My Full Featured Outlook Add-in“, you would set the values like this:

Specifically, the registry key it puts in place is this:
PATH: HKCU\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\addins\equivalentcomaddin
KEY (string/REG_SZ): {OfficeJS GUID}
VALUE: Prog.ID
For example, if I have an Outlook Web Add-in called “My Outlook Add-in” and it has the following manifest entry:
<?xml version="1.0" encoding="UTF-8"?>
<OfficeApp
xmlns="http://schemas.microsoft.com/office/appforoffice/1.1"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0"
xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0"
xsi:type="MailApp">
<Id>c5bc7737-0d79-4302-9e73-2a614941e914</Id>
Let’s say I have a full VSTO add-in called “My Full Featured Outlook Add-in” and it is registered as the following:

If you were to look at the Policy key after it is set you would have an entry like this:
KEY: {c5bc7737-0d79-4302-9e73-2a614941e914}
VALUE: My Full Featured Outlook Add-in
If it were an older traditional COM Add-in, like the top item: AccessAddin.DC, then it would look like this:
KEY: {c5bc7737-0d79-4302-9e73-2a614941e914}
VALUE: AccessAddin.DC
That is all you have to do if you have the newest builds of Outlook for Windows.
NOTE: Coming later in the year, will be an option to add this entry to your Web Add-in Manifest file the way you can with Excel and Word.
NOTE: This is all covered in the latest Office add-ins community call.