I am looking for a tool that I can move cells from one library to another. I have a lot of cells that have to be moved to a different library.
You don't mention what version of MicroStation you're using, so I'll assume it's a flavour of V8. Since a cell library is just a multi-model design file, you can use the tools found in the Models dialog to maintain the models in a file.
I don''t recall if there is a utility that would automate these steps, but this should be enough to get you started.