Using TextEdit I seem to have added by accident some words, which are now not underlined in red when I type. I am willing to edit/delete wrongly spelled custom dictionary words.
You can unlearn a word. Open the Spelling panel: in Textedit, Edit > Spelling > Spelling... (Command-:). Enter the word to forget in the box (the one
under the "
Guess" area). Click Forget.
You could edit the file with TextWrangler, but be sure you know what you are doing. There are invisible characters in that file, and you must get them right. Be sure you have a backup.