I happen to noticed that misc item "misc_hook", when I tried to duplicate it and place it into world. Duplicated misc_hook is obtainable, but default misc_hook is unobtainable, how is it done? I can't find what was changed.

Also I have another problem, that default misc_hook I deleted, seemed to still exist ingame, what cause it?

like .esp files are loaded after .esm files and override them, saves (.ess files) are loaded after .esp and override them. So if you interact with something in game, changes in save (.ess) often override your changes done in CS (that's also why you should always test your mod from a fresh new game first, else conflicts/things not working may be due to a previous save).

Having said that, to clean/modify a save you need something more than CS, take a look at tes3cmd, enchanted editor and for object instances also Mash removers

I had no problem with everything else I modified until I came into this item.

my ESP is last in load list, I even tried start fresh game, it still there.

Tell me if you can delete misc_hook from Ebonheart boat Chun-ook (you can find it hanging bottom lantern next to cabin door), see if it disappear for you ingame?

Deleting the hook works fine for mine. So does looting it in-game. It's just a normal misc item, I don't see why it would be "unobtainable". Perhaps some mod you're using changes it?

I'm sorry, I checked my mod on clean morrowind, misc_hook problem is gone. But I went back to TES Construction, I see one of mod coming from MGSO (plus few extra ones I downloaded) changed misc misc_hook to static furn_hook. I'm not sure which mod did it...

Edit - it's the Unofficial Patch Project 1.6.6