Mereological essentialists argue that mereological summations cannot change their parts. Mereological inessentialists argue that mereological summations can change some or all of their parts. In this paper I articulate and defend a position called Moderate Mereological Inessentialism, according to which certain mereological summations can change some, but not all, of their parts. Persistent mereological summations occur when the functional parts of mereological summations persist through alterations to its spatial parts.