In the Turkish planning system, Urban Development Plan (İmar Planı) represents a "development framework", which assumes the role of a Master Plan, prepared by specialist planners to control all land use decisions, densities and circulation of a city for a target year. It concentrates on the picture of an anticipated future as an end-state. It does not, however, deal with the process between the present and that anticipated future. Consequently, the process of achieving the future is not a matter of concern for "development framework", represented through urban development plans and the Turkish planning system. The planning system endeavors to control every detail during urban development. This gives rise to certainty in the Turkish planning system that leaves no or little discretion and flexibility during plan implementation processes. Owing to its certainty and static nature, the Turkish planning system ignores the possibility of change. The static nature of development plans within the regulatory context of the Turkish planning system cannot provide strategies to manage the dynamic nature of the socio-political context. Furthermore, it causes degradation in the quality of urban space and the public realm. "Management of changes in urban space" is at the very center of the study since those changes might enhance or erode the distinctiveness of a place. It is about shaping the physical form of the city through the control of development rights and depends on the policies about "changes of the urban built environment", defined at five levels in this article. To the extent that possibility of change is disregarded in the Turkish planning system, plan modifications, rather than "management of changes" have become the primary tools of transformation of the urban built environment. They usually emerge through separate actions where individuals begin to produce their own pattern of urbanism in the urban built environment. Within the framework of the study, the plan modifications are analyzed throughout a case study in the city of Mersin. It is taken into account as a field of case study due to its development dynamics. The modern city was founded in the first half of nineteenth century and has been developed rapidly since then. The spatial development has become prominent especially in the last two decades. The rapid development in this period brought about distinctive changes in the spatial context of the city, made Mersin a research field for 'changes in spatial context'. Plan modifications in Mersin are analyzed mainly through three methods of analysis. Simple-statistical analysis focuses on decision outputs. It is the analysis of plan modifications with reference to the 'changes in the spatial context' they caused in the urban built environment. Process-oriented analysis deals with the interactions, and viewpoints of actors taking place in planning control mechanisms. Furthermore, site-specific analysis focuses on the specific examples, brought through the findings of first two analyses. Within data collection frames, concerning simple-statistical analysis, 'changes in the "spatial context' is analyzed via planning data, recorded in the archives of Municipality of Greater Mersin. The study is spatially framed with the borders of Municipality of Greater Mersin and all municipal council records between 1986 and 2003 are gathered in a database, of which the main spine is depending on the typology of plan modifications and their effect on the characteristics of urban built environment. Since all data are recorded digitally on computer, all types of plan modifications and the results of analysis become concrete on maps. The base map during this process is produced with unification of city-wide plans and plan revisions, approved by municipalities in Mersin after 1985. As a further step, within the framework of process-oriented analysis, questionnaires and in-depth interviews are made with actors (the councilors, planning officers, free-lance professionals) taking place in planning process and control mechanisms. Furthermore, the study focused on the specific examples, appeared through the findings of spatialization of data and the interviews. As a matter of fact, the plan modifications might be regarded as the tools to overcome the adaptation problems of the Turkish planning system, since they factually provide a degree of flexibility to manage the transformation of urban space. The study, focusing on plan modifications in the city of Mersin, however, revealed that plan modifications cannot provide such an opportunity. Instead, they reproduce the prevailing problems of the Turkish planning system concerning plot-based understanding of the regulatory context, bureaucratization of control mechanisms in the procedural context and individual actions of the socio-political context. Lessons from other countries such as France, England and the United States of America, illustrated in this study, reveal that the urban development framework depending on solely urban development plans is not able to cope with the changes in the urban built environment. Their planning systems commonly represent supplementary frameworks in order to improve the quality of urban space and the public realm, defined as "design control process". More and more, the problems of the Turkish city are amplified in the inner cities and policies about regeneration of existing stock have to be developed in order to improve the quality of urban space and urban realm. The author conceives the "management of changes in the urban built environment" as an opportunity for the restructuring of the Turkish planning system. In this respect, the author believes that "development framework" of the Turkish planning system should be supplemented by a "design framework" guiding the evolution and transformation of urban form.