I think I’ve got a workaround, but it’s not pretty.
As I understand from this thread (https://community.hubspot.com/t5/HubSpot-Ideas/Trigger-a-workflow-when-a-property-value-has-been-changed/idi-p/4697), if you use the trigger “Is known”, a contact will reenroll every time the property is updated. Because of that, we should be able to make a workflow that can fix this.
Enrollment trigger: Multiple checkbox property “Is knows”
If/then branch: Multiple checkbox property “Has ever been any of X”
If yes: Set property value: Append Multiple checkbox property with X
Now you just need to do this for every option in the series. The contact needs to be guided through each one. Otherwise, it will stop after the first match.
Am I off, or could this work? Please let me know because we are using this solution as of today.