Public facing forms should not have this modification applied.
Even if they change this file ONLY within the local site, all of the forms using HTML Editor on that site will reference this modified file.
It should be noted that the reality is: Whether or not you change the main file, the one you did change (local to the site) will make your public forms less secure on these sites.
All HTMLeditor instances reference this file - public and private - unless you specifiy a different version of the file for each type of location (public / private), which is not the default and must be hand coded.
All the more reason that this should be quickly moved up on the 'things to fix' list - this is now a security issue, which is cause for concern.