You might want to modify an existing driver to optimize the code. In general, you should optimize only those VIs that are called repeatedly in a loop. Configuration VIs generally are called only once and have little effect on application speed.
Follow the Instrument Driver Modification Instructions to modify an existing instrument driver.
If you need to modify only one or two VIs, consider renaming each VI by selecting File»Save As and selecting the Rename option in the Save As dialog box. After you modify the name, you can modify the block diagram and front panel controls. Most changes to the block diagram should affect the String functions.
If you need to modify several VIs and the existing driver is a project-style driver, consider creating a new driver using the existing driver as the starting point. Select Tools»Instrumentation»Create Instrument Driver Project to launch the Create New Instrument Driver Project wizard and create a new driver using the existing driver as the source.
If you intend to submit the modified driver to National Instruments for certification, refer to the NI Developer Zone for more information on Instrument Driver Certification.