This paper focuses on the complications and developmental strategy and approaches for updating legacy systems to MOSA standards. The Department of Defense has adopted Modular Open Systems Approach (MOSA) standards because it lowers risk and accelerates innovation by enabling interoperability between software components. The problem is many existing systems were developed and certified before the MOSA standard was implemented. A solution developed by DornerWorks and Tencate to bring a legacy system up to the MAPS standard is discussed to illustrate this. Tencate the developers of an active blast mitigation system (TenCate ABDSTM) which effectively mitigates launch acceleration, jump height, flight duration and slam-down, caused by IED and mine blast to increase the protection of the vehicle’s occupants. The ABDS was developed to be compliant to the latest DoD standards at the time. Fast forward a couple years and the development of the MOSA based Modular Active Protection System (MAPS) has caused Tencate to adapt their product to a MOSA standard to become MAPS compliant.