This article focuses on the issue of making a kind of preprocessor (called Automatic Modifier of Smalltalk Methods---AMSM) for the programming language Smalltalk. A general algorithm, based on the automatic modification of Smalltalk methods, is proposed. All modifications of related methods are realized in Smalltalk itself. The main parts of method-code and relevant classes are presented. Also, some characteristics (and possible) applications of AMSM are exposed.