Matlab simscape component modification.
There are three steps that are required to include a custom simscape component into simulink


Suitable directory tree structure


Simscape expects component source to be listed in a directory structure prepended with "+" and within the MATLAB search path ( file --> set path)

Take for instance /home/USER/Documents/MATLAB is listed in the MATLAB path search list, I can create a custom simscape file hierarchy from here:

/home/USER/Documents/MATLAB/+custom

Within this new directory I can save my simscape part


Build the simscape part.


With a valid Simscape structure existing, a library part can be "compiled" via the ssc_build command

ssc_build +custom 

where +custom is the structure that was created. This will create within /home/USER/Documents/MATLAB/ a custom_lib.mdl file, a valid Simulink library that can be opened &amp; your custom part dragged out


Adding a custom library to the main library browser


For this to work a slblocks.m file is required 

function blkStruct = slblocks
        % This function specifies that the library should appear
        % in the Library Browser
        % and be cached in the browser repository

        Browser.Library = 'custom_lib';
        % 'mylib' is the name of the library

        Browser.Name = 'My Library';
        % 'My Library' is the library name that appears in the Library Browser

        blkStruct.Browser = Browser;


http://uk.mathworks.com/help/simulink/ug/adding-libraries-to-the-library-browser.html

Your user library and custom part will now appear in the simulink browser