Would be great if I could edit manually the word's strength, today, the system assume that I'm stronger when a new word is acquired, but would be more effective if it assumes that I'm weak instead. And get stronger with practice and if I disagree I could edit it to get better in a specific word I'm having problems.
That would interfere with Duolingo's spaced repetition algorithms. Duolingo doesn't just keep track of whether you've got a question right and whether you needed to peek; it keeps track of how long it is since you saw each word, and aims to show it to you again at a time that will help it stick in your head. If you keep the tree gold, you'll find it works really well.