How can I customize the styles available in the WYSIWYG editor in SharePoint 2010? I'd like to replace the OOTB styles with ones that match our style guide. I found a reference online that mentions editing the form.js and HTMLEditor.js files. Is that the best way to do it? Is it possible to just edit some CSS instead?
I've done something like this for a client, what I did was use IE8 Dev tools to find out the classes used by the Styles applied by the HTMLEditor, make up a CSS file that uses those styles, and set the site's AlternateCSS to use this.
If you can't set the site's Alternate CSS, then you could load in the CSS from the masterpage.
Either way, store the CSS in the Style Library of the site, and you should be able to reference it either way.