I need this until tomorrow means that you have IT in your possession and you need to keep it UNTIL tomorrow. I think ate serves this translation
I need this by tomorrow means that you don't have it in your possession and you need to have it in your possession by(at the latest) tomorrow. If you get it before tomorrow that would be even better. I think just saying preciso disso (no later than tomorrow- don't know how to translate that, so HELPPP lol) conveys that same thought. This is the only one I'm confused on how to translate given your above translations. By and until have two completely different meaning here.
I need this even tomorrow to me means that you have it and you will need it even tomorrow. so you can't let someone have it because you'll need it tomorrow too. I think your translation for that sounds like that's same meaning in Portuguese.
I need this for tomorrow means that you need it specifically for tomorrow. You will need to use it tomorrow. It may or may not be in your possession currently and the person may be asking you when do you need that? and you respond I need this for tomorrow. Para amanha fits I think.
Even though "by" and "until" have different meanings in English, "até" covers both meanings in Portuguese. You get it by the context.
- Preciso disso, mesmo que seja amanhã = I need this, even if it will be ready tomorrow.
- Preciso disso, inclusive amanhã = I have it and I will need it even tomorrow
Until vs by = continuity vs no later than
They aren't interchangeable.
I just want to point out that the help text does not mention this use of "até": "Até: Main meanings: (up) to (some point) - either time or distance Eu vou até o mercado = I go (up) to the market Você tem até três tentativas = You have up to three attempts Until: Ele fica até as seis = He stays until six Even (intensifying): Ate tu, Brutus? = Even you, Brutus?"