Hi there,
It's been explained before that a button nested into MSO A cannot interact or control MSO B, or anything outside MSO A really.
I came across what I would call a hack, that allows the aforementioned situation to work. It requires setting up the button as an achored object in a text frame that is nested in MSO A. This way, you are indeed given the possibility to attribute actions to the anchored button, that impact objects outside of MSO A.
Only problem, it doesn't seem to actually be working once exported in Html... Is there a way to make it work? Is it something that could be enabled in further patches or is it too much of a hack to consider an actual option for "inter-MSO button action"?