Forum Ownership transfer
 

I bought an active forum from someone recently and took over as the administrator as well. He had an expired vbulletin license, so I purchased a new one. What needs to be done to make sure all of the files have MY current license info in them, instead of his old expired license info? Should I expect there to be any issues with any of my current mods or plugins?

You would need to download the version of vbulletin that you are running after logging in with your Customer Number. Then upload those files to the site. Then they will all have the license number on them that are associated with your Customer account.

In doing so, it wont overwrite or mess with any of my plugins, mods or hacks that I am currently running on my site?

Unless you have any custom mod that require manual php file edit in the past. You should have no problem doing it. It works like an normal upgrade.