These are the custom buttons next to the default Uninstall and Disable buttons in the Manage Apps listing for the plugin.
I’m one of the main developers on UPM server, currently I don’t know the answer to this but will invest some time soon to find out for you if there is plugin point you can utilise.
Sorry for the late reply and I’ll update this thread in the near future.
Thanks for your patience, I have looked today and seen that there currently is no way to do this in UPM currently, I have created https://ecosystem.atlassian.net/browse/UPM-6111 which would aim to add this functionality through a plugin point. You can track this issue to get time estimates and updates with regards to the feature requested.
Hope this helps,