Just to explain the process a bit, so you know what should be happening. When you make achange in the Editor interface, it will write those changes to the HTMLEditor/common/insert or update php file but will not create a new file. When you select your stylesheet and styles from within the Editor interface, it writes the styles' names to a new .xml file (insert or update) and writes to the custom/php file the path to where that xml file is, and where the actual stylesheet is.
As this information (style names and location of stylesheet) is the same for both the admin/insert and update pages, the information just needs to be copied to the files from one (insert or update) php page to the other one.
For HTMLEditor in PowerCMS2, although there are javascript files as well as php (and xml) files, the paths only need to be copied to the php pages.
If you wanted to add the styles to PowerStore3 instances of HTMLEditor, the changes would be made/copied in the custom/javascript files.
In SiteSculptor, it would just be to the one 'contents_update_ContentValue1.php' file i.e. - you wouldn't need to do any copying and pasting at all.
If you use the HTMLEditor extension itself to apply an instance of the editor on a page, then the changes would be made to just thecustom/javascript file for that instance.
In every case, when styles are selected, a new custom/xml file is created. All that is required is to make sure that the paths to the correct xml file(s) and stylesheet are present and accurate in either the custom/php or javascript files. It wouldn't hurt (if in doubt) to copy the same lines to both the php and javascript files.