Dude,
When you open MicroStation J...
MicroStation Manager POPS UP, which one selects a file to open.
DON'T OPEN A FILE ... just yet.
Go to ...
FILE>MERGE
Choose "SELECT"
Change the filter from "*.DGN" to "ALL FILES"
Choose your cell libraries.
Then at the bottom screen "Choose the cell to merge to!"
You may need to make a small CELL Library with ONE cell in it.
This one will be your NEW CELL LIBRARY with the mergered libraries.
Then go in and delete that one cell to complete the task!
Good Luck!
Rich