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Design changes are an inevitable part of any product development process. In complex engineered products, changes can cause a cascading effect on other components, commonly known as the “knock-on effect of change”. Managing changes, therefore, has become an important part of design projects. Such changes can propagate through many facets of design and by many different mechanisms. Of particular interest in this dissertation, margins in design play an important role in determining whether a change propagates or gets absorbed. A literature review identifies the underlying concepts of change propagation through a metamodel. The review reveals a lack of study on the mechanisms of change propagation, which greatly dictates how the changes propagate or whether they get absorbed. Based on the insights gained from the literature review, empirical experiments were conducted using student participants. Data from the experiments was collected and analysed using a modelling approach based on a conceptual framework. The analysis of data gave rise to a list of five change propagation mechanisms. The study concluded that margins in a design are one of the most influential factors which determine the nature of propagation when a change is triggered. This dissertation introduces a method called the Margin Value Method to analyse an engineering design, localise the excess margin, and quantify it considering change absorption potential in relation to design performance deterioration. Margin in design may be desirable to mitigate risk and absorb future changes, but at the same time, may be undesirable if the over-specification deteriorates the design’s performance. The Margin Value Method provides guidance for improving a design by prioritising excess margin that provides relatively little advantage at high cost, and could therefore be eliminated to improve design performance. Two case studies using the method are presented.