Why I load Skyrim.esm, Update.esm and few other mods I get strange warnings. These two for example. The rest are very similar.



etc.

After that everything loads. Should I be worried?


And finally, I want to edit certain NPC's by giving them another equipement. For example, I would like to equip Mjoll in Dwarven Armor.

Mjoll -> Inventory -> Default Outfit -> Dwarven Armor

Will that work? Maybe some tips?

Well I think those are normal errors that you get but if you aren't sure you can check here for a list of startup errors that you can ignore. http://www.creationkit.com/Creation_Kit_Startup_Errors

That should work for Mjoll as well.

Ulfric

He has his Default Outfit. What would happen if I'd add to his inventory an Ancient Nord Armor set. Would he wear his old clothes or the armor?

He would not wear Nord Armor unless you changed his default outfit to the nord armor outfit. You could always create an alias for him, and switch his outfits as often as you'd like, but I don't know what the goal of your mod is.

I want to make a mod that would give certain NPC's new armors. I tought about giving Ulfric (the CW version in CK) an Ancient Armor but I also want him to have his outfit as a reward for beating him.

I'm also wondering, if I "tweak" those NPC's, will they return to their proper gear after deleting the mod.

Probably, but someone more knowledgeable than me could probably tell you for sure. I'm not 100% sure what gets saved in your save games anymore. Again, if it were me, I'd make a quest that starts the game enabled, and create aliases for the actors you want to edit.

Yes, once the mod is deleted it will remove the changes that the mod made.