I'm making up the example, but it's a lot simpler than my actual use case: Let's say I've got a table with a large menu of dinner items. I have a column of food preferences (vegetarian, vegan, gluten-free, etc) which is a multi-select field. Now let's say someone points out that it would be a good idea for me to track what options are halaal or kosher. I would like to be able to select all of the menu items that are appropriate and add "kosher" or "halaal" to only those items, without overwriting the current values (vegetarian, etc). What's the best way to do this? I think this would also affect any property that functions like multi-select, most importantly links to another table.