As a tangential side note, in English, we distinguish easily between “which he had not commanded them to do” (not required) and “which he had commanded them not to do” (prohibited) by word order, but in Hebrew no such simple distinction exists. In fact, the Old Testament has no precise equivalent verb to “to prohibit” and elsewhere uses “not to command” in exactly that sense (see Jouon 160k). In Jeremiah 7:31, 19:5 and 32:35 the phrase “which I did not command” (‘ašer lo‘ tsivvîtî) has reference to those who offer their children as burnt offerings on the high places, something specifically prohibited in Leviticus 18:21. This does suggest that Leviticus 10 (along with the Jeremiah passages cited above) are not quite the slam dunk proof texts for the RPW they is sometimes treated as being. As some of the other posts have argued, I think you can still get there from other texts, but its important to make sure that our working is valid as well as our conclusions.