Re: Different image sets
No, there's no need to overwrite the originals. In most cases the icon paths are in the templates, so it's easy to use a theme-specific template to load different icons. See zukakakina.com, for example. In the theme-specific tiki-show_page.tpl, the normal paths to the pagebar icons are replaced with paths to an icon folder in the theme's style directory. (The icons in this case are mostly from here, gferreira_IconsTikiwiki, by the way.) (Also by the way, very soon I will be offering GPL/LGPL themes, etc., at that site, so please stay tuned. 
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You can also change the MyTiki icons by editing the img paths in tiki-mytiki_bar.tpl, the article edit, delete, etc. icons by editing tiki-view_articles.tpl and tiki-read_article.tpl, and so on. Even the smileys used in posts can be added to or replaced by editing their template and uploading new images. (In this case I modified the default template since the same posts appear in all themes.)
-- Gary
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