I don't know how well you understand the Quests and associated scripts that drive the Caravan Leaders (and their followers)? I have done quite a bit of work with them ... but stopped short of actually amending their routes.
When I looked at amending their routes, the conclusion I came to was that it would be better to rebuild the entire system than try to modify what existed.
- The vanilla pathing is quite poor (follow the Solitude/Windhelm one for a day!)
- There is script to cope with the Civil War and what Caravans should do while certain towns are under attack
- The followers do just exactly that, follow behind the leader, only the leader paths
- The campsites are enable/disable Objects that the presense of the Leader activates
If I was going to change where they went ... I would do away with all of it and start again. From what I judged, too much of the existing system was there to get around problems with the existing system ... And so it would be better to start again with a completely new system if you wanted new destinations.
(If you just wanted to change how they got to and from the existing destinations, then there is more chance that modding the existing code will suffice, but again, I think I would still go for a complete rewrite)