I would use the disused: prefix for the old function: http://wiki.openstreetmap.org/wiki/Key:disused: I used at least once disused:amenity=place_of_worship for a church converted into a library: http://www.openstreetmap.org/way/42206561http://www.openstreetmap.org/way/42206561 [edit: See also [other lifecycle prefixes](https://wiki.openstreetmap.org/wiki/Lifecycle_prefix)]

I would use the disused: prefix for the old function: http://wiki.openstreetmap.org/wiki/Key:disused: I used at least once disused:amenity=place_of_worship for a church converted into a library: http://www.openstreetmap.org/way/42206561