It will break it down, better to use regular buttercream on the legs then attach the fondant to that.

If you really want to use royal for the whiteness of the legs, then make your blue trims and images out of royal (thin enough to flow and fill an outline) on wax paper, let them dry completely and attach them to the royal icing covered legs. Make several pieces of each design in case you drop or otherwise break some.

You can also paint on some of the designs with icing color using a thin paintbrush and a little vodka to thin the gel colors. It dries instantly and looks great!