Similar to Language Strings customisation approach, administrators can put modified help files into the local/lang directory, and these files will be used instead of those in the installed language packs.
For example, if you would like to change help for "My friends" page, you can copy htdocs/lang/en.utf8/help/pages/user/myfriends.html to htdocs/local/lang/en.utf8/help/pages/user/myfriends.html and change its content as required. The latter file will override the former one.
Help files for plugins can also be overridden. For example, the help text for "Resume" page, which is originally in htdocs/artefact/resume/lang/en.utf8/help/pages/index.html, can be changed by creating htdocs/local/lang/en.utf8/help/pages/artifact.resume.index.html with desired content.
There is no need to edit the original help files, so updating the site to newer versions of Mahara will be easier - merging local changes to the help files with the updated versions will not be required.