"Alterer" is a slightly uncommon word that refers to someone or something that makes changes or alterations. There are several synonyms that can be used in its place depending on the context. For example, "modifier" can be used to describe someone who alters something in order to improve it. "Adjuster" is another possible synonym, typically used in the context of making small changes to improve fit or function. "Transformer" can be used to describe someone who changes something significantly, while "revamper" might suggest a more thorough and comprehensive set of changes. Other possible synonyms include "manipulator," "tweaker," and "updater," depending on the nature and scope of the changes being made.