Source code for all components may be found in the MCXTRACE library subdirectory of the McXtrace installation; the default is /usr/local/lib/mcxtrace/ on Unix-like systems and C:\mcxtrace\lib on Windows systems, but it may be changed using the MCXTRACE environment variable.
In case users only require to add new features, preserving the existing features of a component, using the EXTEND keyword in the instrument description file is recommended. For larger modification of a component, it is advised to make a copy of the component file into the working directory. A component file in the local directory will in McXtrace takes precedence over a library component of the same name.