Yes, in-house users with Crik-IT admin permissions can do this by clicking on the Tools tab, then the Make Bulk Changes button.  From there, choose Lead Rep from the drop-down menu.  Then choose the rep id you wish to re-assign, and the rep you wish to re-assign the leads to.  Click the Change Lead Rep button.  When Crik-IT has finished re-assigning the leads, it will display a message telling you how many reps have been changed.

Note: the new rep will not get an email alerting them that the leads have been assigned to them.