Specifically, I'm trying to create a symbol that, similar to the 'repeat the previous 4 bars' symbol, will repeat the previous n bars (6 in this example). I've tried duplicating the symbol and editing it, but I don't understand how Sibelius knows what to do with a symbol (and therefore I don't know how its behavior can be edited).
You can concoct a symbol. But if you want playback, I think it will have to be done the old way, the way we used before Sibelius enabled playback of bar repeats. My picture should be self-explanatory.
This sort of query would be better in a specialised forum. www.sibelius.com/cgi-bin/helpcenter/chat/chat.pl?groupid=3