private static HRegion setMobThreshold(HRegion region, byte[] cfName, long modThreshold) {
    ColumnFamilyDescriptor cfd =
      ColumnFamilyDescriptorBuilder.newBuilder(region.getTableDescriptor().getColumnFamily(cfName))
        .setMobThreshold(modThreshold).build();
    TableDescriptor td = TableDescriptorBuilder.newBuilder(region.getTableDescriptor())
      .removeColumnFamily(cfName).setColumnFamily(cfd).build();
    region.setTableDescriptor(td);
    return region;
  }
During compaction, the mob threshold size is changed.
hbase-server/src/test/java/org/apache/hadoop/hbase/mob/TestMobStoreCompaction.java