There are some modifications in the usage purpose of historical structures due to varying needs and changing conditions. However, those modifications can damage the structural system and the system stability. This study focuses on the investigation of the functional effects and usage modifications on the system stability. In this study, three different finite element models of the Hayati Teknecioglu Mansion in Turkey are developed and the seismic responses of the models are investigated. Results of the analyses show that usage modifications might be considered as risky in terms of creating problems for seismic performance.