I think you are referring to zi vs. za and ma vs. mi in Zimal versus Muzzammil. These differences do not change the meaning, because the Arabic language is an Abjad; the language revolves around consonants, not vowels. Zimal and Muzzammil are both derived from one root, Z-M-L, and this decides the meaning of the word. Each root can be turned into dozens of different sounding names, for example Zaamil, Zameel, Zaml, Zameela, Izmil, Zammil, Zamila, Tazammala, etc. Since they all come from the same root, all of them have related meanings.
The meaning of Zimal and Muzzammil are not exactly the same, but they are related. Zimal means "garment", "modesty", and Muzzammil means "dressed in a garment", "covered up in modesty".