All - while I was able to manually change the property values via the API, when it connects into the UI it doesn’t really function in a way that my “brute force” solution is worth documenting and using. Like any exposed data accessible via the API, I changed the property to be one-to-many, but there’s no way to enforce that with the UI so it caused more problems than it potentially solved so I reversed it.
Honestly, this is very close to a “deal-breaker” in terms of being able to fully utilize the Custom Objects within HubSpot.
The other HUGE painpoint is the inability to disallow adding new values - it would be preferable to be able to disable adding in a new entry in some of our COs.
Our rep has heard the message and indicates that HS realizes there is still a lot of work needed with COs … but they’ve demonstrated some pretty good responsiveness over the years.