This disclosure provides a device and method for implementing legacy and improved control functions in controllers, including but not limited to in industrial control systems and other systems. A method includes maintaining, by a device having a controller and a memory, a function library having a plurality of legacy control functions and a plurality of improved control functions. The method includes receiving a process to be executed by the controller. The method includes, when calling a function of the process, determining whether a device setting indicates that the function is to be executed by one of the plurality of improved control functions. The method includes, when the device setting indicates that the function is to be executed by one of the plurality of improved control functions, executing the function using the one of the improved control functions, and otherwise executing the function using one of the legacy control functions.