Start ISSD with ISDC application running. Place a fence around those items you want to tag as breaklines. Be sure to turn OFF any levels you do NOT want tagged as breaklines. Select the Digitize Breakline command from ISDC to make breaklines the "active" feature. In the MicroStation command window key in "fc fence tag". Click a data on the view to process the fence contents. Done. Note that this works as well for obscure areas, or any other tag.
Caviat: To fence tag random points as mass points, place a fence around the points. From the ISDC menu use the Custom Edit Active Area Define From Fence command. Then use Custom Edit Fence Tag As Mass Points.