Is there a way from CK/script to make the game forget the last ridden horse (make the horse stop follow/teleport)?
What I want to do is "park" your favorite horse like Frost and Shadowmere at HF stables.
Bonus: should be compatible with mods like CH but I could research on that if I found how to do it on vanilla first.

The closest I ever came to finding a solution to this is to ride a "Conjured" horse like Arvak which gets deleted when the spell ends.

Never tinkered with followers myself but you might want to have a look at http://www.youtube.com/watch?v=xO6BIZO7oO0 video, it shows the basics on making an animal follower. It should at least give you a rough n idea on how to alter the default follower behavior.

Yes, I know of that, actually do you know if you need to ride it or summon is enough?
I wonder if I can use activate() on a horse that I placeAtMe() disabled then kill it? I will try this but don't have CK near right now...I was hoping for something more straight from the box.

Not the behavior would be my problem, but make the horse forget it was the last ridden.

Haven't tried it, but what happens if you simply clear the player horse alias? Does it then still make that horse fast travel with you?

Hmm, i have to look closely but seeing the Game#GetPlayerLastRidenHorse() and Actor#IsPlayerLastRiddenHorse() I mostly assumed is an engine thing, not an quest driven mechanic, or at last there will be leftovers in the engine and compatibility issues unless I address the root.