Harmony info

[Gladiozzo]

Hello everyone, I've been following the forum for some time, thanks to the guides I found here I was able to create some mods. Initially by modifying the existing xml files and then creating them from 0. Over time and with tools like dnspy I was able to add features to the game that cannot be obtained with xml files. Now I would like to bring these changes as mods, and I thought the only possible way could be harmony. From what I understand, however, harmony can change the result via prefix and postfix. Is there a way to modify the methods with a custom code? For example by inserting the custom code in place of the existing one?

(I state that I am not a programmer and everything I managed to do I did it only for passion, I apologize in advance if the question seems stupid)