This chapter proposes a solution that provides reliable, non-disruptive updates to critical systems using a novel design pattern called a “snap-in,” which is able to install replacement routines embedded in shared libraries during system execution. Most system updates are performed in a static or maintenance state. However, dynamically updating software reduces the time required for adding functionality and applying security upgrades. The proposed snap-in solution improves on previous work by adopting the novel approach of using the target’s application binary interface to first load shared libraries that contain replacement routines into a running application, supplanting the original routines with replacement routines without having to modify the existing code. An automated toolkit is provided for scanning application binaries and determining where the replacement routines are to be added.