Probably yet another stupid question from me but I need to understand this. I have a word that i know well but where one of the characters definition just slips my brain all the time. If I mark it as not study that character in that word, will it also prevent the character to be studied if i later on add it as a real word? I will probably not remember that i ever have marked it as not study before so the risk is that that word then never will be studied as a word, or?

If you add the character again later, it will come back. This is true of any item you delete: Skritter will remember your progress on the item once you re-add it.