Change HTML on certain pages

Is it possible to change the HTML content on certain pages? I would like to be able to add instructions on how to use the file manager for end users who may not be so tech savvy that they exactly know what everything is when they need to move from / to /some/folder/path.


I did find /usr/local/$usermin/ that session_login.cgi is editable - wondering if this is safe to edit or if there are reference spots that I can edit the ‘failed’ array (assuming it’s an array, not used perl before) to include a custom fail reason and show a message that corresponds to that reason.