Configuring Synchronization using Input / Mapping file?

Inherited a new Domain.  Need to migrate the users from this new domain (Domain A) to our existing domain (Domain B)

We did not use Migration Manager to create the user accounts in Domain B.

We used our own process to set those up.  Then using a mapping file into ADMT we merged attributes across from Domain A to Domain B (including passwords and SIDHistory).

Quest MM is a newly purchased product for us.  The thought was to user Quest MM's Synchronize ability to keep the objects in Domain B up to date.  Specifically when user changes password in Domain A we want it transferred to Domain B.

It would seem to me that the most straightforward way of doing this would be to use a mapping file so we can specifically say to merge this object with that object.  But not seeing how to do that.  Is it possible?

As I mentioned I am new to Quest MM so I apologize if this is a super simple question.

Thanks very much