Updating LIST property using update_property_link

I am trying to add a value to a custom property, which should be a LIST.

Unfortunately, the list is overwritten by the value I entered in the link - instead of the value being appended to the list.

I have googled and searched this forum, finding some older posts about this - and no solution. Hopefully something has happened during the 2-3 years since last post about it :)

Is it in anyway possible to add a value to a property of type LIST when clicking a link in an email? I looked into the flow solution, using segments. But you can’t trigger a flow when a profile has been updated so … 

Any ideas?