Hi Juli,
You can do this with a smart campaign, custom field, and some tokens.
You have:
Product Interest and Area of Interest, and you'll need to create a custom field.
Basically, you're going to take the value from Product Interest, the one you want to "win" in the end, and move it to a temporary field. This will save the value, but also allow you to write to Product Interest without fear of losing what was there. Then you you can use a smart campaign to write both the values from Product Interest(now in the custom field) and Area of Interest back into the original Product Interest field.
You can do this with a smart campaign set up like this:
Smart List Flow
Product Interest > Is Not Empty Change Data Value (New Custom Field Name) > New Value is {{lead.Product Interest}}
(This gets all leads with a value in that field) (This will move the value from Product Interest to the new custom field)
Once this campaign has run you can then create the campaign below to combine the fields and put the values back into the Product Interest field.
Smart List Flow
Product Interest > Is Not Empty Change Data Value (Product Interest) > New Value is {{lead.(custom field name)}} + {{lead.Area of Interest}}
(To get the same members) (This will overwrite the Production Interest field with the two values in the other fields, one of which is the
same Product Interest value. You can separate the two values however you like, the the "+" can be a dash or
comma.)
Let me know if you have any questions on this.
John