I have a Many-to-Many editor linked into my Affiliate Company entity (company/org). This M-to-M relationship is so we can class them as multiple types as a multi-selection.  

Now in the UI, this translates to a middle step in authoring for the entity. Here I can select 1-N values from the Collection Picker, which is great for creating the many-2-many links. 
 



In this case though the mapping table containing the ID’s from both parents also has it’s own attribute, IsPrimaryType, to tell us what the *main* type for the company is. I can expose the value on the Collection attribute list, but it does not want to let me check the box to set the attribute to True for the one I want…do you know if there is a way to get the interface to allow this to be edited…is it just read only because it requires an override or something else?