If you buy a new towbar and it was EU type approved with a spacer then it will come with a spacer. If it wasn't approved with a spacer then you cannot legally fit one.
You can remove the spacer and fit something else of equivalent thickness, a bracket for a Bulldog stabiliser for example or a bracket for carrying bicycles. You cannot, though, fit anything thicker than the spacer it was originally approved with.
I would agree with Tim.. Honda did not make the tow bracket, the tow bracket manufacturer almost always tests the bar with a 25mm spacer. 25mm then is the 'designed' maximum you can go to and so includes any other plates between mounting flange and towball flange.
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