"1.4.5 The weight that is measured at the mainsail hoist height of a mast lying perfectly horizontal with its base supported at the bottom edge of the mast section is referred to as the "mast tip weight". The minimum mast tip weight of a fully fitted mast, excluding standing rigging, is set at 6.00 kg for reasons of seaworthiness and to guarantee fair racing."

This is confusing to me, but I don't think any weight is actually added. Rather, a mast is either legal or it isn't, when weighed in the manner mentioned above.