Oh it’s fine, now that I realized ALL IN ONE SEO plugin was causing the non-saving issue (see my previous comment): I can now insert any shortcode, like a revslider shortcode, so I can have a revslider at the top of my category page :0) Love it !!!
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Otherwise: I already just asked this question as a separate entry, as I thought it could be useful to other people in other contexts than just the shop,.. but here I go again:
Can a Static Block be placed somewhere using shortcode ?