Midchuck, it has to do with the spirit of the thing. Are you playing along with your friend, or performing with them? If you're playing pre-arranged accompaniments & harmonies you're performing. If no one else is playing along (or harmonizing), will it feel to the other listeners as if you are playing along? Or as if you are just doing more of your group's music?

It ain't illegal. Just not in accord, IMO, with the feeling of a good singaround.

I have occasionally seen members of quite well known groups ask whether anyone minded if they did a group song in a singaround rather than lead an individual song. They didn't all sing group songs and they didn't sing them on every round. I think that was good etiquette. Besides we got to hear some great songs we'd never have heard otherwise....

Rita F