"Agregarle" it's the correct word for it (both es_es & es_la). "Agregarlo" would be correct if you are referencing an object (it's a 'loísmo', using -lo instea

"Agregarle" it's the correct word for it (both es_es & es_la). "Agregarlo" would be correct if you are referencing an object (it's a 'loísmo', using -lo instead of -le when referencing people). - Also, in Spain we refer to 'snowboarding' just as 'snowboard' (for the snowboard itself and for the activity)