you mean when a sport club allows other people to rent their building for parties ? I would still not map it as a events_venue. The primary purpose is still club home. Of course there will be cases where a building is a club home 50% of the time and 50% of the time an event venue, but they are rare, not ?

You can always place 2 nodes within the building, or map the primary purpose on the building and the secondary as node inside.