You can move Password Manager to a new server without having the users re-register. Here are the steps to move Password Manager to a new server:
1) Launch the PMADmin site on the existing server and create and Export file (general settings-> import/export)
2) copy that export file over to the new server along with the pw for that file
3) Install Password Manager on the new server
4) launch the PMADmin site and at the initialization screen select "Unique instance"
5) once in the PMAdmin site on the new server select import general settings-> import/export and browse to the Export file you copied from the old server.
Once the site is up and running please turn off the old service (Password Manager) on the original server until you are happy with the server is up and runnin