editing ship hull masses in the xml files not working, unable to change them, how do i do so?

So, I copied the xml files to the example mod folder and pasted the XML files in, and edited the hull mass to what I wanted (nothing too extreme, at most increased one by around 200) and when I relaunched the game and went into the menu ship editor the changes hadn't taken, idk why and how exactly do you go about doing this?