There is an easy way! At least for re-assignable Objects like Projects and Tasks. Like the previous comment said, go ahead and reactivate them first to a free restricted level license.
Go to the Search field in the upper right of the screen, and click the dropdown, then Advanced Search at the bottom of the list.
For Projects:
Select "Projects" in the column on the left.
Select "Filter Your Results"
Select "Project>>Owner ID"
Type in the person's name who owns the original projects.
Click Update Results.
Select all of the projects en mass by clicking the checkbox at the top of the list to the left of "Name".
Click the Edit button that appears just above that.
The "Project Owner" field will appear about 7 fields down. Enter the new owner's name.
Select Save Changes.
You can do the same for any Object that you can change the owner on.
This will not work for Reports or Dashboards, which is the problem I'm facing right now. You have to Copy them, and Sharing doesn't copy over, so it needs to be manually set on the new objects. Once you're all done, then you can deactivate them.
Hope this helps! Alexis McMullen -------------