The intent is for Aric to incorporate them into the expansion itself, but anyone is free to use the code. Each file corresponds to one of the add-ons (calling it that because they are not standalone and rely on aric’s expansion mod).
Within each file the code is broken down into sections by the file edited and then either one new code or modified code. Modified code replaces a variable or function while new code adds it.
If you don’t know what your doing you really should make sure you have a backup of your files before attempting anything (probably a good idea even if you do know what your doing). The files are formatted like this so it is easier for Aric (or anyone for that matter) to review exactly what is being changed and walk through the code.