Note, in my CI/CD process I have a private and public version of each extension (set of tasks), the former is used for functional testing within the CD process, the latter is the one everyone can see.
So, this meant I had two public versions of the same extension, confusing.
Turns out you can’t change a public extension back to be private, either via the UI or by uploading a corrected VSIX. Also you can’t delete any public extension that has ever been downloaded, and my previously private one had been downloaded once, by me for testing.
So my only option was to un-publish the previously private extension so only the correct version was visible in the public marketplace.
This meant I had to also alter my CI/CD process to change the extensionID of my private extension so I could publish a new private version of the extension.
Luckily, as all the GUIDs for the tasks within the extension did not change once I had installed the new version of the extension I had mispublished in my test VSTS instance my pipeline still worked.
Only downside is I am left with an un-publish ‘dead’ version listed in my private view of the marketplace. This is not a problem, just does not look ‘neat and tidy’