vBulletin does not allow any sort of custom ranks that users can upload and use, as they have to be implemented and setup using the Admin panels and such. There is however a possible way of uploading a secondary set of ranks and such that could apply to a certain member usergroup once someone were to reach the post count requirement for the group. Say for example, someone moves up from Senior member to Veteran Member, or "Been here to Long..." status and that particular member group could use a separate ranking system... But it kind of defeats the purpose since once you reach a certain number of posts and enter into the specific member category the ranks change for higher post counts anyway. In that case it would be more prudent just to add additional ranks in there.
-SkyeWelse