Our diocese mandates that each parish have 24-hour Exposition on a designated day each month, for vocations. Thus there is always Exposition at one or more Churches in the Diocese.
At the mass after which the Exposition ,in our parish, the host is replaced with a freshly consecrated one. The one removed is broken up and added to the Communion hosts.
[We also have a parish mandated weekly 24-hour Exposition, but that would be too frequent a changing.]