If I understand your question correctly, I think the answer is that it is not possible to do this. Or maybe a better answer is that it doesn’t work quite in that way.
Not everyone agrees with the way I describe RM’s Shared Facts feature. But the way I think of it is that RM doesn’t actually support shared facts. By that, I mean that you can’t enter a fact for one person and then share that fact with another person in the sense that you are just making a copy of the original fact for the other person. Rather, you assign roles to facts and then when you go through RM’s Shared Facts dialog to share the fact, what you are really sharing is the roles. For example, roles for the Marriage fact might be such thing as BestMan, FlowerGirl, or Minister. The BestMan, FlowerGirl, and Minister did not get married that day. So it’s not the Marriage fact that’s getting shared. It’s the specific role they played at the wedding that’s getting shared.
Seen in this light, facts have notes and roles have notes. The fact note applies only to the fact itself and not to any of its subordinate roles. When you do a Share operation in the Edit Person screen and select a role, there is a note for the role that you can fill in.
What does get shared between a fact and its subordinate roles are the following items: the date, the sort date, the place, the place details, he proof indicator, the primary indicator, the private indicator, all citations, all media, and all tasks. What does not get shared between a fact and its subordinate roles is the sentence and the note. There is a fact sentence and a fact note. There is a role sentence and a role note. Even the sentence variables work very differently between the fact sentence and the role sentence.
For my Marriage example, in the sentence for the Marriage fact itself, variables such as [BestMan], [FlowerGirl], and [Minister] can appear, such as <[BestMan] was the best man.> or <[Flowergirl] was the flower girl.>. But in the role sentences, the role names do not appear. Rather, you use the [ThisPerson] variable. For example, the sentence for the BestMan role might be something like <[ThisPerson] was the best man at the wedding of [Couple][Date][Place].>