The modern Cyber Security threat environment is highly dynamic with constant changes in threat sources, threat vectors, and threat motivations. Static approaches to Cyber Security become less effective over time and product lifecycles of meeting the security requirements and information protection needs of a system. This problem becomes more significant with the added complexity of the numerous information exchanges and dependencies inherent in most systems of systems, which is coupled with relatively short supported lifecycles of many software and computer hardware products. Frequent refresh or version updates in software and hardware components require continuous reassessment of the effective Cyber Security posture against an ever changing threat environment. Further, practical time and resource limitations constrain the rigor that is acceptable in the application of formal Systems Engineering practices in initial system design, development, and acquisition. This has the effect of pushing much of the system cost for Cyber Security into the operations and maintenance phases of the product lifecycle, which is also typically highly constrained regarding time and resources and is also challenged with maintaining a properly trained and skilled human workforce. This paper will discuss the impact of the economical application of key System Engineering processes at various stages of a product lifecycle in order to enhance the effective Cyber Security of a product in a dynamic threat environment. The dynamic nature of the threat environment and internal volatility of Information Technology systems require System Engineering processes to be tailored specifically to address change in the most cost effective and time sensitive manner. This includes internal system change during updates and component refresh and external change in the threat environment in which the system operates. The challenge is to effectively manage change to systems with complex internal and external interactions while maintaining a security posture relevant to a current threat environment while keeping complexity within the capability of the workforce to implement. As both the system internal components and the external environment change, the mapping of system security functions and capabilities to the current and potential threat space becomes a significant problem of complexity management in the understanding of the effects of change mapped against the system posture and external threats. However, the emphasis and rigorous application of several key System Engineering processes supporting change management and tailored to the system and environment can make the application of Cyber Security both more effective and more cost effective over the lifecycle of the product. This paper describes several key areas in the product lifecycle where modest investments in Systems Engineering processes have the potential to reduce security related expenditures over time and potentially extend the time until a system becomes cost prohibitive to maintain an effective security posture or a security breach occurs due to a failure in design, implementation, or validation.