I know there have been numerous posts about this piece but I wonder if that's because the maority of teachers aren't teaching it properly.
In any case, I am an adult learner and I have had multiple teachers, because they were not teaching me any technique. While I was trying to learn Prelude in C, I was told that none of the notes should sound louder than the others. However, exactly how to do this, was not fully explained. I experimented but never quite got it. How is this done?
Never take anyone's teachings as absolute in any way. No one knows what the hell they are doing(basically). Simply take it as a suggestion as someone else mentioned. There is absolutely no right and wrong in music. Ok, there might be but don't worry about it.
There is no natural law in music that says if you do it wrong you will be struck by lightning. Most humans are quite insane and think they have everything figure out and if you don't listen to them then they hate you. (it's some god complex + fear + ...)
Music is progressive, like all things. You get better the more you do it. Practice makes perfect is not an adage, it effectively is the "absolute way" I said don't worry about. The more you learn the more you see everything. It's like putting a puzzle together. At first you don't know where any pieces go but with a lot of work or luck you make a few chunks. Over time more and more pieces start to come together(this is basically topology at work and yoneda is the larger "big picture" understanding that forms).
You have to experiment. Why not try both ways? If you are told X is right and Y is wrong you either trust it on blind faith without having any clue why(and maybe the person saying it doesn't even know) or you try Y and X and compare them.
Now, in some things it is important that you not do Y. E.g., jumping off a 100ft cliff may be wrong unless you have a hang glider and are properly strapped in and have some experience. In music, you can always do Y. (that is one of the great things) Pretty much you cannot get hurt doing Y. Some will say it can ruin your technique, cause muscle problems, etc. None of it is true unless you are only doing Y. If you are doing X and Y then you will eventually realize X is better or Y is. You also will develop that internal compass to make such judgements.
When we are practicing piano it isn't just about memorizing notes and putting our fingers down. That is the first step but after you have them you start trying other things. That is the joy that comes from actually making music rather than recreating it. If you want to make music, you do variations and experimentations.
So, you say "What if I do that" and you try it. Then you get better for trying it.
You say "Ok, I want to do that, how do I do it?" and then you spend an hour or 10 weeks trying to figure it out. You are better for doing it.
A teacher can help and a teacher can hurt and they can do both at the same time. But you should never be afraid or resist experimenting with things in music. That is part of the fun.
E.g., In your case, you try it with dynamics and without. You then find out which one you like better. It is about figuring out what you like and figuring out how to achieve it.
If someone says "DON'T DO IT, DO IT THIS WAY" they are trying to impose upon you want they like. That isn't right. They are just being insane. In some sense they just want to control you or get you to listen to them. It isn't about them, it is about you. Now, if you are playing for them, as if you were cooking dinner for them, then you do it the way they want. But since you are taking lessons from them so you can play for yourself you do what you want. Of course you do need to listen to them because they may actually know something but you don't treat it as the word of god. Of course if they are demanding you do it their way and not showing you why it is better then likely they are a bad teacher.
My suggestion is that you sit at the piano for about 5 hours experimenting with various things in that piece. It is a great piece to experiment with. You can do about a millions things with it. You can learn a lot. This is the point of the piece. Bach is teaching you something. Do you know what it is? I bet you don't. If you spend a few years playing all the time you will understand what he is teaching. Bach is a great teacher! He teaches music without any words, the best way to learn! [Of course all the masters were like this. They knew that the way to learn music was with music, not words]
Topic: Bach Prelude in C