Post Management

Hey all, looking for some suggestions on a task that is going to take a while if I have to do it through the classic WP setup.

Scenario:
I just moved my WP from one site to another (no major issues), but I had a small little problem with my categories and was getting a 404 error. I fixed all of that, but I have added some new categories and would like to go through and reassign some posts to the new categories that better fit, but it is very slow going and was curious if there is a better way via a plugin or something.?

Task:
Would like to be able to easily/quickly reassign the categories of pre-existing posts.

Thanks,
Andy