How can residents allow outsiders to participate as volunteers?

Our board decided that guests or outsiders from another community cannot participate or volunteer at events from another adult comunity.

For example; ensemble of guitar players including 3 players from another adult community will perform at our community. The Association said the outsiders cannot rehease or perform in our community, although the event was sanctioned by our association in the past, and had outsiders performing.

Another example, a piano player moved out of our community and was told he can no longer accompany the singers; however, we can pay that person and that's OK.

What can residents do to allow guest/outsider participation?